By adopting the differential age method, we select 17 832 luminous red galaxies from the Sloan Digital Sky Survey Data Release Seven covering redshift 0 〈 z 〈 0.4 to measure the Hubble parameter. Using the full spec...By adopting the differential age method, we select 17 832 luminous red galaxies from the Sloan Digital Sky Survey Data Release Seven covering redshift 0 〈 z 〈 0.4 to measure the Hubble parameter. Using the full spectrum fitting package UZySS, these spectra are reduced with single stellar population models and optimal age information from our selected sample is derived. With the decreasing age-redshift relation, four new observational H（z） data （OHD） points are obtained, which are H（z） = 69.0 ± 19.6 km s^-1 Mpc^-1 at z = 0.07, H（z） = 68.6± 26.2 km s^-1 Mpc^-1 at z = 0.12, H（z）=72.9 ± 29.6 km s^-1 Mpc^-1 at z = 0.2 and H（z）=88.8 ± 36.6 km s^-1 Mpc^-1 at z = 0.28, respectively. Combined with 21 other available OHD data points, the performance of the constraint on both flat and non-flat ACDM models is presented.展开更多
Detection of γ-ray emissions from a class of active galactic nuclei （viz blazars）, has been one of the important findings from the Compton Gamma-Ray Observatory （CGRO）. However, their γ-ray luminosity function h...Detection of γ-ray emissions from a class of active galactic nuclei （viz blazars）, has been one of the important findings from the Compton Gamma-Ray Observatory （CGRO）. However, their γ-ray luminosity function has not been well determined. Few attempts have been made in earlier works, where BL Lacs and Flat Spectrum Radio Quasars （FSRQs） have been considered as a single source class. In this paper, we investigated the evolution and γ-ray luminosity function of FSRQs and BL Lacs separately. Our investigation indicates no evolution for BL Lacs, however FSRQs show significant evolution. Pure luminosity evolution is assumed for FSRQs and exponential and power law evolution models are examined. Due to the small number of sources, the low luminosity end index of the luminosity function for FSRQs is constrained with an upper limit. BL Lac luminosity function shows no signature of break. As a consistency check, the model source distributions derived from these luminosity functions show no significant departure from the observed source distributions.展开更多
We have collected all available spectra and photometric data from the SDSS catalog for bright AGNs complied from the first three months of the Fermi large area telescope all-sky survey. Based on the 106 high-confidenc...We have collected all available spectra and photometric data from the SDSS catalog for bright AGNs complied from the first three months of the Fermi large area telescope all-sky survey. Based on the 106 high-confidence and 11 low-confidence associated bright AGN list, the photometry data are collected from SDSS DR7 for 28 sources （12 BL Lacs and 16 FSRQs）, two of which are low-confidence associated bright AGNs. Among these 28 SDSS photometric sources, SDSS spectra are available for 20 sources （6 BL Lacs and 14 FSRQs）. The black hole masses MBH and the broad line region （BLR） luminosity were obtained for 14 FSRQs by measuring the line-widths and strengths of broad emission lines from the SDSS spectra. The broad emission line measurements of five FSRQs are presented for the first time in this work. The optical continuum emission of these 14 FSRQs is found to be likely dominated by the non-thermal jet emission by comparing the relationship between the broad Mg II line and continuum luminosity to that of radio-quiet AGNs. The black hole mass of the 14 FSRQs ranges from 10^8.2 M⊙ to 10^9.9 M⊙, with most of the sources larger than 10^9 M⊙. The Eddington ratio Lbol/LEdd ranges from 10-1＇5 to - 1. This implies that an optically thin, geometrically thick accretion disk may exist in these FSRQs.展开更多
We present a quantitative study of the classification of Extremely Red Objects （EROs）. The analysis is based on the multi-band spatial- and ground-based observations （HST/ACS-BViz, HST/NICMOS-JH, VLT-JHK） in the H...We present a quantitative study of the classification of Extremely Red Objects （EROs）. The analysis is based on the multi-band spatial- and ground-based observations （HST/ACS-BViz, HST/NICMOS-JH, VLT-JHK） in the Hubble Ultra Deep Field （UDF）. Over a total sky area of 5.50 arcmin2 in the UDF, we select 24 EROs with the color criterion （i - K）vega 〉 3.9, corresponding to （I - K）vega 〉 ～4.0, down to Kvega = 22. We develop four methods to classify EROs into Old passively evolving Galaxies （OGs） and Dusty star-forming Galaxies （DGs）, including （i - K） vs. （J - K） color diagram, spectral energy distribution fitting method, Spitzer MIPS 24 um image matching, and nonparametric measure of galaxy morphology, and found that the classification results from these methods agree well. Using these four classification methods, we classify our EROs sample into 60Gs and 8 DGs to KVega 〈 20.5, and 80Gs and 16 DGs to KVega 〈 22, respectively. The fraction of DGs increases from 8/14 at KVega 〈 20.5 to 16/24 at KVega 〈 22. TO study the morphology of galaxies with its wavelength, we measure the central concentration and the Gini coefficient for the 24 EROs in our sample in HST/ACS-i, z and HST/NICMOS-J, H bands. We find that the morphological parameters of galaxies in our sample depend on the wavelength of observation, which suggests that caution is necessary when comparing single wavelength band images of galaxies at a variety of redshifts.展开更多
Using a simple color selection based on B-, z- and K-band photometry, BzK =（z - K）AB - （B - Z）AB 〉 -0.2, we picked out 52 star-forming galaxies at 1.4 ≤z ≤ 2.5 （sBzKs） from a K-band selected sample （Kvega 〈...Using a simple color selection based on B-, z- and K-band photometry, BzK =（z - K）AB - （B - Z）AB 〉 -0.2, we picked out 52 star-forming galaxies at 1.4 ≤z ≤ 2.5 （sBzKs） from a K-band selected sample （Kvega 〈 22.0） in an area of - 5.5 arcmin^2 of the Hubble Ultra Deep Field （UDF）. We develop a new photometric redshift method, and the error in our photometric redshifts is less than 0.02（1 ＋ z）. From the photometric redshift distribution, we find the BzK color criterion can be used to select star-forming galaxies at 1.4≤ z ≤ 2.5 with Kvega 〈 22.0. Down to Kvega 〈 22.0, the number counts of sBzKs increase linearly with the K magnitude; the sBzKs are strongly clustered, and most of them have irregular morphologies on the ACS images. They have a median reddening of E（B - V） - 0.28, an average star formation rate of - 36 M⊙ yr^-1 and a typical stellar mass of - 10^10 M⊙. The UV criterion for the galaxies at z - 2 can select most of the faint sBzKs in the UDF, but it does not work well for bright, massive, highly-reddened, actively star-forming galaxies.展开更多
This study presents results on detecting neutral atomic hydrogen(H I)21 cm absorption in the spectrum of PKS PKS1413+13 at redshift z=0.24670041.The observation was conducted by FAST,with a spectral resolution of10 Hz...This study presents results on detecting neutral atomic hydrogen(H I)21 cm absorption in the spectrum of PKS PKS1413+13 at redshift z=0.24670041.The observation was conducted by FAST,with a spectral resolution of10 Hz,using 10 minutes of observing time.The global spectral profile is examined by modeling the absorption line using a single Gaussian function with a resolution of 10 kHz within a 2 MHz bandwidth.The goal is to determine the rate of the latest cosmic acceleration by directly measuring the redshift evolution of the H I 21 cm absorption line with Hubble flow toward a common background quasar over a decade or longer time span.This will serve as a detectable signal generated by the accelerated expansion of the Universe at redshift z<1,referred to as redshift drift z(5)or the SL effect.The measured H I gas column density in this DLA system is approximately equivalent to the initial observation value,considering uncertainties of the spin temperature of a spiral host galaxy.The high signal-to-noise ratio of 57,obtained at a 10 kHz resolution,strongly supports the feasibility of using the H I 21 cm absorption line in DLA systems to accurately measure the redshift drift rate at a precision level of around 10~(-10)per decade.展开更多
The extragalactic diffuse emission at γ-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could ...The extragalactic diffuse emission at γ-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could originate from either truly diffuse processes or from unresolved point sources such as AGNs, normal galaxies and starburst galaxies. Here, we examine the unresolved point source origin of the extragalactic γ-ray background emission from normal galaxies and starburst galaxies. γ-ray emission from normal galaxies is primarily coming from cosmic-ray interactions with interstellar matter and radiation （-90%） along with a small contribution from discrete point sources （-10%）. Starburst galaxies are expected to have enhanced supernovae activity which leads to higher cosmic-ray densities, making starburst galaxies sufficiently luminous atγ-ray energies to be detected by the current γ-ray mission （Fermi Gamma-ray Space Telescope）.展开更多
The origin of the extragalactic gamma-ray background （EGRB） is still an open question, even nearly forty years after its discovery. The emission could originate either from truly diffuse processes or from unresolved...The origin of the extragalactic gamma-ray background （EGRB） is still an open question, even nearly forty years after its discovery. The emission could originate either from truly diffuse processes or from unresolved point sources. Although the majority of the 271 point sources detected by EGRET （Energetic Gamma Ray Experiment Telescope） are unidentified, of the identified sources, blazars are the dominant candidates. Therefore, unresolved blazars may be considered the main contributor to the EGRB, and many studies have been carried out to understand their distribution, evolution and contribution to the EGRB. Considering that γ-ray emission comes mostly from jets of blazars and that the jet emission decreases rapidly with increasing jet to line-of-sight angle, it is not surprising that EGRET was not able to detect many large inclination angle active galactic nuclei （AGNs）. Though Fermi could only detect a few large inclination angle AGNs during the first three months of its survey, it is expected to detect many such sources in the near future. Since non-blazar AGNs are expected to have higher density as compared to blazars, these could also contribute significantly to the EGRB. In this paper, we discuss contributions from unresolved discrete sources including normal galaxies, starburst galaxies, blazars and off-axis AGNs to the EGRB.展开更多
The spectral energy distribution (SED) of the γ-ray flare observed inJuly 1997 in BL Lacertae is re-considered. It is pointed out that the optical observa-tions made by Webb et al. showed the associated optical flare...The spectral energy distribution (SED) of the γ-ray flare observed inJuly 1997 in BL Lacertae is re-considered. It is pointed out that the optical observa-tions made by Webb et al. showed the associated optical flare has a hard spectrum(the average spectral index αopt～ 0.48, F_v∝v^(-α)), and the ASCA observationsmade by Tanihata et al. showed very steep spectra in the soft X-ray band (0.7-1.5 keV) (α_x～3-4). We find that the flux densities and spectral indices in both theoptical and soft X-ray bands are closely consistent with a ‘canonical' synchrotronspectrum emitted by relativistic electrons of a power-law energy distribution witha high energy cutoff, and thus the peak of the SED of the synchrotron radiation (inrepresentation of vF_v) is located in the EUV -- soft X-ray bands. Therefore, theGeV γ-ray emission observed in the July 1997 outburst may be mainly due to thesynchrotron self-Compton (SSC) process, contrasting with the current explanationsin terms of external radiation Compton (ERC) process, in which the seed photonsare mostly taken to be the UV emission from the clouds of the broad emission lineregion. We argue that the hard optical spectra observed during the γ-ray outburstmay be an important signature for the acceleration of high energy electrons (γ_e～10~4)in the γ-ray emitting region.展开更多
Theory and observations concerning the cosmic reionization epoch are briefly discussed in the context of recent observations attributed to dark matter. A case is made that cold ground state interstellar atomic hydroge...Theory and observations concerning the cosmic reionization epoch are briefly discussed in the context of recent observations attributed to dark matter. A case is made that cold ground state interstellar atomic hydrogen of average density of about one atom per cubic centimeter (1.67 × 10-21?kg·m-3?or 1.67 × 10-24?g·cm-3) appears to be the most likely candidate to explain these observations.展开更多
We investigate the cross-correlation between galaxy clusters and QSOs using Sloan Digital Sky Survey （SDSS） DR4 - 5000 deg^2 data. With photometric redshifts of galaxies, we select galaxy clusters based on the local...We investigate the cross-correlation between galaxy clusters and QSOs using Sloan Digital Sky Survey （SDSS） DR4 - 5000 deg^2 data. With photometric redshifts of galaxies, we select galaxy clusters based on the local projected densities of LRGs brighter than Mr′ = -22. The QSOs are from the main sample of SDSS QSO spectroscopic survey to i′ = 19. A significant positive correlation is found between the clusters and QSOs. Under the assumption that the signal is caused by gravitational lensing, we fit the signal with singular isothermal sphere （SIS） model and NFW profile halo model. The velocity dispersion σv = 766 km s^-1 is derived for the best-fit of SIS model. Best-fit for the NFW model requires the dark matter halo mass within 1.5 h^-1 Mpc to be 4.6 × 10^14 h^-1 M⊙. The mass parameter Ωcl of the cluster sample is deduced as 0.077 with the SIS model and 0.083 with the NFW model. Our results of Ωcl are smaller than those given by Croom ＆ Shanks and by Myers et al.展开更多
In order to test the systematics of the Amati relation, 24 long-duration GRBs with available Eγ,iso and Ep are separated into two subgroups according to the B-band luminosity of their host galaxies. The Amati relatio...In order to test the systematics of the Amati relation, 24 long-duration GRBs with available Eγ,iso and Ep are separated into two subgroups according to the B-band luminosity of their host galaxies. The Amati relations in the two subgroups are found to be in agreement with each other within the uncertainties. Taking into account of the well established luminosity - metallicity relation of galaxies, no strong evolution of the Amati relation with the GRB＇s environmental metaUicity is implied in this study.展开更多
As the advent of precision cosmology,the Hubble constant(H0)inferred from the Lambda Cold Dark Matter fit to the Cosmic Microwave Background data is increasingly in tension with the measurements from the local distanc...As the advent of precision cosmology,the Hubble constant(H0)inferred from the Lambda Cold Dark Matter fit to the Cosmic Microwave Background data is increasingly in tension with the measurements from the local distance ladder.To approach its real value,we need more independent methods to measure,or to make constraint of,the Hubble constant.In this paper,we apply a plain method,which is merely based on the Friedman-Lema??tre-Robertson-Walker cosmology together with geometrical relations,to constrain the Hubble constant by proper motions of radio components observed in AGN twin-jets.Under the assumption that the ultimate ejection strengths in both sides of the twin-jet concerned are intrinsically the same,we obtain a lower limit of H0,min=51.5±2.3 km s^(-1)Mpc^(-1) from the measured maximum proper motions of the radio components observed in the twin-jet of NGC 1052.展开更多
We present a simulation experiment of a pipeline based on machine learning algorithms for neutral hydrogen(H I)intensity mapping(IM)surveys with different telescopes.The simulation is conducted on H I signals,foregrou...We present a simulation experiment of a pipeline based on machine learning algorithms for neutral hydrogen(H I)intensity mapping(IM)surveys with different telescopes.The simulation is conducted on H I signals,foreground emission,thermal noise from instruments,strong radio frequency interference(s RFI),and mild RFI(m RFI).We apply the Mini-Batch K-Means algorithm to identify s RFI,and Adam algorithm to remove foregrounds and m RFI.Results show that there exists a threshold of the s RFI amplitudes above which the performance of our pipeline enhances greatly.In removing foregrounds and m RFI,the performance of our pipeline is shown to have little dependence on the apertures of telescopes.In addition,the results show that there are thresholds of the signal amplitudes from which the performance of our pipeline begins to change rapidly.We consider all these thresholds as the edges of the signal amplitude ranges in which our pipeline can function well.Our work,for the first time,explores the feasibility of applying machine learning algorithms in the pipeline of IM surveys,especially for large surveys with the next-generation telescopes.展开更多
The China Space Station Telescope(CSST) photometric survey aims to perform a high spatial resolution(~0.″ 15)photometric imaging for the targets that cover a large sky area(~17,500 deg^(2)) and wide wavelength range(...The China Space Station Telescope(CSST) photometric survey aims to perform a high spatial resolution(~0.″ 15)photometric imaging for the targets that cover a large sky area(~17,500 deg^(2)) and wide wavelength range(from NUV to NIR). It expects to explore the properties of dark matter, dark energy, and other important cosmological and astronomical areas. In this work, we evaluate whether the filter design of the Multi-channel Imager(MCI), one of the five instruments of the CSST, can provide accurate photometric redshift(photoz) measurements with its nine medium-band filters to meet the relevant scientific objectives. We generate the mock data based on the COSMOS photometric redshift catalog with astrophysical and instrumental effects. The application of upper limit information of low signal-to-noise ratio data is adopted in the estimation of photoz. We investigate the dependency of photoz accuracy on the filter parameters, such as band position and width. We find that the current MCI filter design can achieve good photoz measurements with accuracy σ_(z)■ 0.017 and outlier fraction f_(c)■ 2.2%. It can effectively improve the photoz measurements of the main CSST survey using the Survey Camera to an accuracy σ_(z)■ 0.015 and outlier fraction f_(c)■ 1.5%. This indicates that the original MCI filters are proper for the photoz calibration.展开更多
We present a large sample of candidate galaxies at z ≈ 7 - 10, selected in the Hubble Ultra Deep Field using the new observations of the Wide Field Camera 3 that was recently installed on the Hubble Space Telescope. ...We present a large sample of candidate galaxies at z ≈ 7 - 10, selected in the Hubble Ultra Deep Field using the new observations of the Wide Field Camera 3 that was recently installed on the Hubble Space Telescope. Our sample is composed of 20 z850-dropouts （four new discoveries）, 15 Y105-dropouts （nine new discoveries） and 20 J125-dropouts （all new discoveries）. The surface densities of the Z850-dropouts are close to what was predicted by earlier studies, however, those of the Y105- and J125-dropouts are quite unexpected. While no Y105- or J125-dropouts have been found at AB ≤ 28.0 mag, their surface densities seem to increase sharply at fainter levels. While some of these candidates seem to be close to foreground galaxies and thus could possibly be gravitationally lensed, the overall surface densities after excluding such cases are still much higher than what would be expected if the luminosity function does not evolve from z ～ 7 to 10. Motivated by such steep increases, we tentatively propose a set of Schechter function parameters to describe the luminosity functions at z ≈8 and 10. As compared to their counterpart at z ≈ 7, here L^＊ decreases by a factor of ～ 6.5 and Ф^＊ increases by a factor of 17-90. Although such parameters are not yet demanded by the existing observations, they are allowed and seem to agree with the data better than other alternatives. If these luminosity functions are still valid beyond our current detection limit, this would imply a sudden emergence of a large number of low-luminosity galaxies when looking back in time to z ≈ 10, which, while seemingly exotic, would naturally fit in the picture of the cosmic hydrogen reionization. These early galaxies could easily account for the ionizing photon budget required by the reionization, and they would imply that the global star formation rate density might start from a very high value at z ≈ 10, rapidly reach the minimum at z≈ 7, and start to rise again towards z ≈ 6. In this scenario, the majority of th展开更多
We forecast the cosmological constraints of the neutral hydrogen(HI) intensity mapping(IM)technique with radio telescopes by assuming 1-year of observational time. The current and future radio telescopes that we consi...We forecast the cosmological constraints of the neutral hydrogen(HI) intensity mapping(IM)technique with radio telescopes by assuming 1-year of observational time. The current and future radio telescopes that we consider here are Five-hundred-meter Aperture Spherical radio Telescope(FAST), Baryon acoustic oscillations In Neutral Gas Observations(BINGO), and Square Kilometre Array phase Ⅰ(SKA-Ⅰ) single-dish experiments. We also forecast the combined constraints of the three radio telescopes with Planck. We find that the 1σ errors of(w0, wa) for BINGO, FAST and SKA-Ⅰ with respect to the fiducial values are respectively,(0.9293, 3.5792),(0.4083, 1.5878) and(0.3158, 0.4622). This is equivalent to(56.04%, 55.64%) and(66.02%, 87.09%) improvements in constraining(w0, wa) for FAST and SKA-Ⅰ respectively relative to BINGO. Simulations further show that SKA-Ⅰ will put more stringent constraints than both FAST and BINGO when each of the experiments is combined with Planck measurements. The 1σ errors for(w0, wa), BINGO + Planck, FAST + Planck and SKA-Ⅰ + Planck covariance matrices are respectively(0.0832, 0.3520),(0.0791, 0.3313) and(0.0678, 0.2679) implying there is an improvement in(w0, wa) constraints of(4.93%, 5.88%) for FAST + Planck relative to BINGO + Planck and an improvement of(18.51%, 23.89%) in constraining(w0, wa) for SKA-Ⅰ + Planck relative to BINGO + Planck. We also compared the performance of Planck data plus each single-dish experiment relative to Planck alone,and find that the reduction in(w0, wa) 1σ errors for each experiment plus Planck, respectively, imply the(w0, wa) constraints improvement of(22.96%, 8.45%),(26.76%, 13.84%) and(37.22%, 30.33%) for BINGO + Planck, FAST + Planck and SKA-Ⅰ + Planck relative to Planck alone. For the nine cosmological parameters in consideration, we find that there is a trade-off between SKA-Ⅰ and FAST in constraining cosmological parameters, with each experiment being more superior in constraining a particular set of parameters.展开更多
We build a sample of 298 spectroscopically-confirmed galaxies at redshift z - 2, selected in the z850-band from the GOODS-MUSIC catalog. By utilizing the rest frame 8 p.m luminosity as a proxy of the star formation ra...We build a sample of 298 spectroscopically-confirmed galaxies at redshift z - 2, selected in the z850-band from the GOODS-MUSIC catalog. By utilizing the rest frame 8 p.m luminosity as a proxy of the star formation rate （SFR）, we check the accuracy of the standard SED-fitting technique, finding it is not accurate enough to provide reliable estimates of the physical parameters of galaxies. We then develop a new SED-fitting method that includes the IR luminosity as a prior and a generalized Calzetti law with a variable Rv. Then we exploit the new method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar masses and ages. We find that there is a general trend of increasing attenuation with the SFR. Moreover, we find that the SFRs range between a few to 103 M~ yr-1, the masses from 109 to 4 ~ 1011 Mo, and the ages from a few tens of Myr to more than 1 Gyr. We discuss how individual age measurements of highly attenuated objects indicate that dust must have formed within a few tens of Myr and already been copious at 〈 100 Myr. In addition, we find that low luminosity galaxies harbor, on average, significantly older stellar populations and are also less massive than brighter ones; we discuss how these findings and the well known ＇downsizing＇ scenario are consistent in a framework where less massive galaxies form first, but their star formation lasts longer. Finally, we find that the near-IR attenuation is not scarce for luminous objects, contrary to what is customarily assumed; we discuss how this affects the interpretation of the observed M,/L ratios.展开更多
We collect the second Large Area Telescope AGN catalog （2LAC） and Monitor of Jets in AGN with VLBA Equipment （MOJAVE） quasi-simultaneous data to investigate the radio-γ connection of blazars. The cross sample con...We collect the second Large Area Telescope AGN catalog （2LAC） and Monitor of Jets in AGN with VLBA Equipment （MOJAVE） quasi-simultaneous data to investigate the radio-γ connection of blazars. The cross sample contains 166 sources. The statistical analysis based on this sample confirms positive correlations between these two bands, but the correlations become weaker as the γ-ray energy increases. The statistical results between various parameters show negative correla- tions of γ-ray photon spectral index with γ-ray loudness for both Flat Spectrum Radio Quasars （FSRQs） and BL Lacertae objects, positive correlations of γ-ray variability index with the γ-ray loudness for FSRQs, a negative correlation of the γ-ray variabil- ity index with the γ-ray photon spectral index for FSRQs, and negative correlations of γ-ray photon spectral index with γ-ray luminosity for FSRQs. These results suggest that the γ-ray variability may be due to changes inside the γ-ray emission region like the injected power, rather than changes in the photon density of the external radiation fields, and the variability amplitude tends to be larger as the γ-rays are closer to the high energy peak of the spectral energy distribution （SED）. No correlation of variabil- ity index found for BL Lacertae objects implies that variability behavior may differ below and above the peak energy.展开更多
基金supported by the National Natural Science Foundation of China
文摘By adopting the differential age method, we select 17 832 luminous red galaxies from the Sloan Digital Sky Survey Data Release Seven covering redshift 0 〈 z 〈 0.4 to measure the Hubble parameter. Using the full spectrum fitting package UZySS, these spectra are reduced with single stellar population models and optimal age information from our selected sample is derived. With the decreasing age-redshift relation, four new observational H（z） data （OHD） points are obtained, which are H（z） = 69.0 ± 19.6 km s^-1 Mpc^-1 at z = 0.07, H（z） = 68.6± 26.2 km s^-1 Mpc^-1 at z = 0.12, H（z）=72.9 ± 29.6 km s^-1 Mpc^-1 at z = 0.2 and H（z）=88.8 ± 36.6 km s^-1 Mpc^-1 at z = 0.28, respectively. Combined with 21 other available OHD data points, the performance of the constraint on both flat and non-flat ACDM models is presented.
文摘Detection of γ-ray emissions from a class of active galactic nuclei （viz blazars）, has been one of the important findings from the Compton Gamma-Ray Observatory （CGRO）. However, their γ-ray luminosity function has not been well determined. Few attempts have been made in earlier works, where BL Lacs and Flat Spectrum Radio Quasars （FSRQs） have been considered as a single source class. In this paper, we investigated the evolution and γ-ray luminosity function of FSRQs and BL Lacs separately. Our investigation indicates no evolution for BL Lacs, however FSRQs show significant evolution. Pure luminosity evolution is assumed for FSRQs and exponential and power law evolution models are examined. Due to the small number of sources, the low luminosity end index of the luminosity function for FSRQs is constrained with an upper limit. BL Lac luminosity function shows no signature of break. As a consistency check, the model source distributions derived from these luminosity functions show no significant departure from the observed source distributions.
基金supported by the National Natural Science Foundation of China (Grant Nos.10633010, 10703009, 10833002, 10773020 and 10821302)the 973 Program (No. 2009CB824800)+1 种基金the CAS (KJCX2-YW-T03)supported by the Yunnan Provincial Science Foundation of China (grant 2008CD061)
文摘We have collected all available spectra and photometric data from the SDSS catalog for bright AGNs complied from the first three months of the Fermi large area telescope all-sky survey. Based on the 106 high-confidence and 11 low-confidence associated bright AGN list, the photometry data are collected from SDSS DR7 for 28 sources （12 BL Lacs and 16 FSRQs）, two of which are low-confidence associated bright AGNs. Among these 28 SDSS photometric sources, SDSS spectra are available for 20 sources （6 BL Lacs and 14 FSRQs）. The black hole masses MBH and the broad line region （BLR） luminosity were obtained for 14 FSRQs by measuring the line-widths and strengths of broad emission lines from the SDSS spectra. The broad emission line measurements of five FSRQs are presented for the first time in this work. The optical continuum emission of these 14 FSRQs is found to be likely dominated by the non-thermal jet emission by comparing the relationship between the broad Mg II line and continuum luminosity to that of radio-quiet AGNs. The black hole mass of the 14 FSRQs ranges from 10^8.2 M⊙ to 10^9.9 M⊙, with most of the sources larger than 10^9 M⊙. The Eddington ratio Lbol/LEdd ranges from 10-1＇5 to - 1. This implies that an optically thin, geometrically thick accretion disk may exist in these FSRQs.
基金supported by the National Natural Science Foundation of China (NSFC, Nos. 10573014, 10633020 and 10873012)the Knowledge InnovationProgram of the Chinese Academy of Science (No. KJCX2-YW-T05)National Basic ResearchProgram of China (973 Program) (No. 2007CB815404).
文摘We present a quantitative study of the classification of Extremely Red Objects （EROs）. The analysis is based on the multi-band spatial- and ground-based observations （HST/ACS-BViz, HST/NICMOS-JH, VLT-JHK） in the Hubble Ultra Deep Field （UDF）. Over a total sky area of 5.50 arcmin2 in the UDF, we select 24 EROs with the color criterion （i - K）vega 〉 3.9, corresponding to （I - K）vega 〉 ～4.0, down to Kvega = 22. We develop four methods to classify EROs into Old passively evolving Galaxies （OGs） and Dusty star-forming Galaxies （DGs）, including （i - K） vs. （J - K） color diagram, spectral energy distribution fitting method, Spitzer MIPS 24 um image matching, and nonparametric measure of galaxy morphology, and found that the classification results from these methods agree well. Using these four classification methods, we classify our EROs sample into 60Gs and 8 DGs to KVega 〈 20.5, and 80Gs and 16 DGs to KVega 〈 22, respectively. The fraction of DGs increases from 8/14 at KVega 〈 20.5 to 16/24 at KVega 〈 22. TO study the morphology of galaxies with its wavelength, we measure the central concentration and the Gini coefficient for the 24 EROs in our sample in HST/ACS-i, z and HST/NICMOS-J, H bands. We find that the morphological parameters of galaxies in our sample depend on the wavelength of observation, which suggests that caution is necessary when comparing single wavelength band images of galaxies at a variety of redshifts.
基金Supported by the National Natural Science Foundation of China.
文摘Using a simple color selection based on B-, z- and K-band photometry, BzK =（z - K）AB - （B - Z）AB 〉 -0.2, we picked out 52 star-forming galaxies at 1.4 ≤z ≤ 2.5 （sBzKs） from a K-band selected sample （Kvega 〈 22.0） in an area of - 5.5 arcmin^2 of the Hubble Ultra Deep Field （UDF）. We develop a new photometric redshift method, and the error in our photometric redshifts is less than 0.02（1 ＋ z）. From the photometric redshift distribution, we find the BzK color criterion can be used to select star-forming galaxies at 1.4≤ z ≤ 2.5 with Kvega 〈 22.0. Down to Kvega 〈 22.0, the number counts of sBzKs increase linearly with the K magnitude; the sBzKs are strongly clustered, and most of them have irregular morphologies on the ACS images. They have a median reddening of E（B - V） - 0.28, an average star formation rate of - 36 M⊙ yr^-1 and a typical stellar mass of - 10^10 M⊙. The UV criterion for the galaxies at z - 2 can select most of the faint sBzKs in the UDF, but it does not work well for bright, massive, highly-reddened, actively star-forming galaxies.
基金supported by the National SKA Program of China(2022SKA0110202)the National Natural Science Foundation of China(grants No.11929301)。
文摘This study presents results on detecting neutral atomic hydrogen(H I)21 cm absorption in the spectrum of PKS PKS1413+13 at redshift z=0.24670041.The observation was conducted by FAST,with a spectral resolution of10 Hz,using 10 minutes of observing time.The global spectral profile is examined by modeling the absorption line using a single Gaussian function with a resolution of 10 kHz within a 2 MHz bandwidth.The goal is to determine the rate of the latest cosmic acceleration by directly measuring the redshift evolution of the H I 21 cm absorption line with Hubble flow toward a common background quasar over a decade or longer time span.This will serve as a detectable signal generated by the accelerated expansion of the Universe at redshift z<1,referred to as redshift drift z(5)or the SL effect.The measured H I gas column density in this DLA system is approximately equivalent to the initial observation value,considering uncertainties of the spin temperature of a spiral host galaxy.The high signal-to-noise ratio of 57,obtained at a 10 kHz resolution,strongly supports the feasibility of using the H I 21 cm absorption line in DLA systems to accurately measure the redshift drift rate at a precision level of around 10~(-10)per decade.
基金supported by a project (Grant No.SR/S2/HEP12/2007)the Department of Space and Technology, India.
文摘The extragalactic diffuse emission at γ-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could originate from either truly diffuse processes or from unresolved point sources such as AGNs, normal galaxies and starburst galaxies. Here, we examine the unresolved point source origin of the extragalactic γ-ray background emission from normal galaxies and starburst galaxies. γ-ray emission from normal galaxies is primarily coming from cosmic-ray interactions with interstellar matter and radiation （-90%） along with a small contribution from discrete point sources （-10%）. Starburst galaxies are expected to have enhanced supernovae activity which leads to higher cosmic-ray densities, making starburst galaxies sufficiently luminous atγ-ray energies to be detected by the current γ-ray mission （Fermi Gamma-ray Space Telescope）.
基金supported by a project (Grant No. SR/S2/HEP12/2007) funded by DST,India
文摘The origin of the extragalactic gamma-ray background （EGRB） is still an open question, even nearly forty years after its discovery. The emission could originate either from truly diffuse processes or from unresolved point sources. Although the majority of the 271 point sources detected by EGRET （Energetic Gamma Ray Experiment Telescope） are unidentified, of the identified sources, blazars are the dominant candidates. Therefore, unresolved blazars may be considered the main contributor to the EGRB, and many studies have been carried out to understand their distribution, evolution and contribution to the EGRB. Considering that γ-ray emission comes mostly from jets of blazars and that the jet emission decreases rapidly with increasing jet to line-of-sight angle, it is not surprising that EGRET was not able to detect many large inclination angle active galactic nuclei （AGNs）. Though Fermi could only detect a few large inclination angle AGNs during the first three months of its survey, it is expected to detect many such sources in the near future. Since non-blazar AGNs are expected to have higher density as compared to blazars, these could also contribute significantly to the EGRB. In this paper, we discuss contributions from unresolved discrete sources including normal galaxies, starburst galaxies, blazars and off-axis AGNs to the EGRB.
文摘The spectral energy distribution (SED) of the γ-ray flare observed inJuly 1997 in BL Lacertae is re-considered. It is pointed out that the optical observa-tions made by Webb et al. showed the associated optical flare has a hard spectrum(the average spectral index αopt～ 0.48, F_v∝v^(-α)), and the ASCA observationsmade by Tanihata et al. showed very steep spectra in the soft X-ray band (0.7-1.5 keV) (α_x～3-4). We find that the flux densities and spectral indices in both theoptical and soft X-ray bands are closely consistent with a ‘canonical' synchrotronspectrum emitted by relativistic electrons of a power-law energy distribution witha high energy cutoff, and thus the peak of the SED of the synchrotron radiation (inrepresentation of vF_v) is located in the EUV -- soft X-ray bands. Therefore, theGeV γ-ray emission observed in the July 1997 outburst may be mainly due to thesynchrotron self-Compton (SSC) process, contrasting with the current explanationsin terms of external radiation Compton (ERC) process, in which the seed photonsare mostly taken to be the UV emission from the clouds of the broad emission lineregion. We argue that the hard optical spectra observed during the γ-ray outburstmay be an important signature for the acceleration of high energy electrons (γ_e～10~4)in the γ-ray emitting region.
文摘Theory and observations concerning the cosmic reionization epoch are briefly discussed in the context of recent observations attributed to dark matter. A case is made that cold ground state interstellar atomic hydrogen of average density of about one atom per cubic centimeter (1.67 × 10-21?kg·m-3?or 1.67 × 10-24?g·cm-3) appears to be the most likely candidate to explain these observations.
文摘We investigate the cross-correlation between galaxy clusters and QSOs using Sloan Digital Sky Survey （SDSS） DR4 - 5000 deg^2 data. With photometric redshifts of galaxies, we select galaxy clusters based on the local projected densities of LRGs brighter than Mr′ = -22. The QSOs are from the main sample of SDSS QSO spectroscopic survey to i′ = 19. A significant positive correlation is found between the clusters and QSOs. Under the assumption that the signal is caused by gravitational lensing, we fit the signal with singular isothermal sphere （SIS） model and NFW profile halo model. The velocity dispersion σv = 766 km s^-1 is derived for the best-fit of SIS model. Best-fit for the NFW model requires the dark matter halo mass within 1.5 h^-1 Mpc to be 4.6 × 10^14 h^-1 M⊙. The mass parameter Ωcl of the cluster sample is deduced as 0.077 with the SIS model and 0.083 with the NFW model. Our results of Ωcl are smaller than those given by Croom ＆ Shanks and by Myers et al.
文摘In order to test the systematics of the Amati relation, 24 long-duration GRBs with available Eγ,iso and Ep are separated into two subgroups according to the B-band luminosity of their host galaxies. The Amati relations in the two subgroups are found to be in agreement with each other within the uncertainties. Taking into account of the well established luminosity - metallicity relation of galaxies, no strong evolution of the Amati relation with the GRB＇s environmental metaUicity is implied in this study.
基金supported by the National Natural Science Foundation of China(No.11903002)the Research Project of Baise University(No.2019KN04)。
文摘As the advent of precision cosmology,the Hubble constant(H0)inferred from the Lambda Cold Dark Matter fit to the Cosmic Microwave Background data is increasingly in tension with the measurements from the local distance ladder.To approach its real value,we need more independent methods to measure,or to make constraint of,the Hubble constant.In this paper,we apply a plain method,which is merely based on the Friedman-Lema??tre-Robertson-Walker cosmology together with geometrical relations,to constrain the Hubble constant by proper motions of radio components observed in AGN twin-jets.Under the assumption that the ultimate ejection strengths in both sides of the twin-jet concerned are intrinsically the same,we obtain a lower limit of H0,min=51.5±2.3 km s^(-1)Mpc^(-1) from the measured maximum proper motions of the radio components observed in the twin-jet of NGC 1052.
基金supported by the National Natural Science Foundation of China under Grants 61872099 and 62272116。
文摘We present a simulation experiment of a pipeline based on machine learning algorithms for neutral hydrogen(H I)intensity mapping(IM)surveys with different telescopes.The simulation is conducted on H I signals,foreground emission,thermal noise from instruments,strong radio frequency interference(s RFI),and mild RFI(m RFI).We apply the Mini-Batch K-Means algorithm to identify s RFI,and Adam algorithm to remove foregrounds and m RFI.Results show that there exists a threshold of the s RFI amplitudes above which the performance of our pipeline enhances greatly.In removing foregrounds and m RFI,the performance of our pipeline is shown to have little dependence on the apertures of telescopes.In addition,the results show that there are thresholds of the signal amplitudes from which the performance of our pipeline begins to change rapidly.We consider all these thresholds as the edges of the signal amplitude ranges in which our pipeline can function well.Our work,for the first time,explores the feasibility of applying machine learning algorithms in the pipeline of IM surveys,especially for large surveys with the next-generation telescopes.
基金the support of NSFC-11822305, NSFC-11773031, NSFC-11633004, MOST-2018YFE0120800, MOST-2020SKA0110402, and CAS Interdisciplinary Innovation Teamsupported by the science research grants from the China Manned Space Project with NO.CMSCSST-2021-B01 and CMS-CSST-2021-A01. Z.Y.Z+1 种基金support by the National Natural Science Foundation of China (11773051 and 12022303)the CAS Pioneer Hundred Talents Program。
文摘The China Space Station Telescope(CSST) photometric survey aims to perform a high spatial resolution(~0.″ 15)photometric imaging for the targets that cover a large sky area(~17,500 deg^(2)) and wide wavelength range(from NUV to NIR). It expects to explore the properties of dark matter, dark energy, and other important cosmological and astronomical areas. In this work, we evaluate whether the filter design of the Multi-channel Imager(MCI), one of the five instruments of the CSST, can provide accurate photometric redshift(photoz) measurements with its nine medium-band filters to meet the relevant scientific objectives. We generate the mock data based on the COSMOS photometric redshift catalog with astrophysical and instrumental effects. The application of upper limit information of low signal-to-noise ratio data is adopted in the estimation of photoz. We investigate the dependency of photoz accuracy on the filter parameters, such as band position and width. We find that the current MCI filter design can achieve good photoz measurements with accuracy σ_(z)■ 0.017 and outlier fraction f_(c)■ 2.2%. It can effectively improve the photoz measurements of the main CSST survey using the Survey Camera to an accuracy σ_(z)■ 0.015 and outlier fraction f_(c)■ 1.5%. This indicates that the original MCI filters are proper for the photoz calibration.
基金supported in part by the NASA JWST Interdisciplinary Scientist grant NAG5-12460 from GSFC
文摘We present a large sample of candidate galaxies at z ≈ 7 - 10, selected in the Hubble Ultra Deep Field using the new observations of the Wide Field Camera 3 that was recently installed on the Hubble Space Telescope. Our sample is composed of 20 z850-dropouts （four new discoveries）, 15 Y105-dropouts （nine new discoveries） and 20 J125-dropouts （all new discoveries）. The surface densities of the Z850-dropouts are close to what was predicted by earlier studies, however, those of the Y105- and J125-dropouts are quite unexpected. While no Y105- or J125-dropouts have been found at AB ≤ 28.0 mag, their surface densities seem to increase sharply at fainter levels. While some of these candidates seem to be close to foreground galaxies and thus could possibly be gravitationally lensed, the overall surface densities after excluding such cases are still much higher than what would be expected if the luminosity function does not evolve from z ～ 7 to 10. Motivated by such steep increases, we tentatively propose a set of Schechter function parameters to describe the luminosity functions at z ≈8 and 10. As compared to their counterpart at z ≈ 7, here L^＊ decreases by a factor of ～ 6.5 and Ф^＊ increases by a factor of 17-90. Although such parameters are not yet demanded by the existing observations, they are allowed and seem to agree with the data better than other alternatives. If these luminosity functions are still valid beyond our current detection limit, this would imply a sudden emergence of a large number of low-luminosity galaxies when looking back in time to z ≈ 10, which, while seemingly exotic, would naturally fit in the picture of the cosmic hydrogen reionization. These early galaxies could easily account for the ionizing photon budget required by the reionization, and they would imply that the global star formation rate density might start from a very high value at z ≈ 10, rapidly reach the minimum at z≈ 7, and start to rise again towards z ≈ 6. In this scenario, the majority of th
基金the DAAD (German Academic Exchange Service) scholarshipfinancial support from The African Institute for Mathematical Sciences, University of KwaZulu-Natal+1 种基金The Dar Es Salaam University College of Education, Tanzaniasupport from the National Research Foundation of South Africa (Grant Nos. 105925 and 110984)
文摘We forecast the cosmological constraints of the neutral hydrogen(HI) intensity mapping(IM)technique with radio telescopes by assuming 1-year of observational time. The current and future radio telescopes that we consider here are Five-hundred-meter Aperture Spherical radio Telescope(FAST), Baryon acoustic oscillations In Neutral Gas Observations(BINGO), and Square Kilometre Array phase Ⅰ(SKA-Ⅰ) single-dish experiments. We also forecast the combined constraints of the three radio telescopes with Planck. We find that the 1σ errors of(w0, wa) for BINGO, FAST and SKA-Ⅰ with respect to the fiducial values are respectively,(0.9293, 3.5792),(0.4083, 1.5878) and(0.3158, 0.4622). This is equivalent to(56.04%, 55.64%) and(66.02%, 87.09%) improvements in constraining(w0, wa) for FAST and SKA-Ⅰ respectively relative to BINGO. Simulations further show that SKA-Ⅰ will put more stringent constraints than both FAST and BINGO when each of the experiments is combined with Planck measurements. The 1σ errors for(w0, wa), BINGO + Planck, FAST + Planck and SKA-Ⅰ + Planck covariance matrices are respectively(0.0832, 0.3520),(0.0791, 0.3313) and(0.0678, 0.2679) implying there is an improvement in(w0, wa) constraints of(4.93%, 5.88%) for FAST + Planck relative to BINGO + Planck and an improvement of(18.51%, 23.89%) in constraining(w0, wa) for SKA-Ⅰ + Planck relative to BINGO + Planck. We also compared the performance of Planck data plus each single-dish experiment relative to Planck alone,and find that the reduction in(w0, wa) 1σ errors for each experiment plus Planck, respectively, imply the(w0, wa) constraints improvement of(22.96%, 8.45%),(26.76%, 13.84%) and(37.22%, 30.33%) for BINGO + Planck, FAST + Planck and SKA-Ⅰ + Planck relative to Planck alone. For the nine cosmological parameters in consideration, we find that there is a trade-off between SKA-Ⅰ and FAST in constraining cosmological parameters, with each experiment being more superior in constraining a particular set of parameters.
基金Supported by the National Natural Science Foundation of China
文摘We build a sample of 298 spectroscopically-confirmed galaxies at redshift z - 2, selected in the z850-band from the GOODS-MUSIC catalog. By utilizing the rest frame 8 p.m luminosity as a proxy of the star formation rate （SFR）, we check the accuracy of the standard SED-fitting technique, finding it is not accurate enough to provide reliable estimates of the physical parameters of galaxies. We then develop a new SED-fitting method that includes the IR luminosity as a prior and a generalized Calzetti law with a variable Rv. Then we exploit the new method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar masses and ages. We find that there is a general trend of increasing attenuation with the SFR. Moreover, we find that the SFRs range between a few to 103 M~ yr-1, the masses from 109 to 4 ~ 1011 Mo, and the ages from a few tens of Myr to more than 1 Gyr. We discuss how individual age measurements of highly attenuated objects indicate that dust must have formed within a few tens of Myr and already been copious at 〈 100 Myr. In addition, we find that low luminosity galaxies harbor, on average, significantly older stellar populations and are also less massive than brighter ones; we discuss how these findings and the well known ＇downsizing＇ scenario are consistent in a framework where less massive galaxies form first, but their star formation lasts longer. Finally, we find that the near-IR attenuation is not scarce for luminous objects, contrary to what is customarily assumed; we discuss how this affects the interpretation of the observed M,/L ratios.
基金the National Natural Science Foundation of China (Grant Nos. 10903025, 10973034, 11103060 and 11133006) for financial supportthe support of the National Basic Research Program of China (973 Program, 2009CB824800)
文摘We collect the second Large Area Telescope AGN catalog （2LAC） and Monitor of Jets in AGN with VLBA Equipment （MOJAVE） quasi-simultaneous data to investigate the radio-γ connection of blazars. The cross sample contains 166 sources. The statistical analysis based on this sample confirms positive correlations between these two bands, but the correlations become weaker as the γ-ray energy increases. The statistical results between various parameters show negative correla- tions of γ-ray photon spectral index with γ-ray loudness for both Flat Spectrum Radio Quasars （FSRQs） and BL Lacertae objects, positive correlations of γ-ray variability index with the γ-ray loudness for FSRQs, a negative correlation of the γ-ray variabil- ity index with the γ-ray photon spectral index for FSRQs, and negative correlations of γ-ray photon spectral index with γ-ray luminosity for FSRQs. These results suggest that the γ-ray variability may be due to changes inside the γ-ray emission region like the injected power, rather than changes in the photon density of the external radiation fields, and the variability amplitude tends to be larger as the γ-rays are closer to the high energy peak of the spectral energy distribution （SED）. No correlation of variabil- ity index found for BL Lacertae objects implies that variability behavior may differ below and above the peak energy.
