- ID:
- ivo://CDS.VizieR/J/MNRAS/478/5336
- Title:
- z-low satellite galaxies in COSMOS survey
- Short Name:
- J/MNRAS/478/5336
- Date:
- 10 Dec 2021 14:18:30
- Publisher:
- CDS
- Description:
- Faint dwarf satellite galaxies are important as tracers of small-scale structure, but remain poorly characterized outside the Local Group, due to the difficulty of identifying them consistently at larger distances. We review a recently proposed method for estimating the average satellite population around a given sample of nearby bright galaxies, using a combination of size and magnitude cuts (to select low-redshift dwarf galaxies preferentially) and clustering measurements (to estimate the fraction of true satellites in the cut sample). We test this method using the high-precision photometric redshift catalogue of the COSMOS survey, exploring the effect of specific cuts on the clustering signal. The most effective of the size-magnitude cuts considered recover the clustering signal around low-redshift primaries (z<0.15) with about two-thirds of the signal and 80 per cent of the signal-to-noise ratio obtainable using the full COSMOS photometric redshifts. These cuts are also fairly efficient, with more than one-third of the selected objects being clustered satellites. We conclude that structural selection represents a useful tool in characterizing dwarf populations to fainter magnitudes and/or over larger areas than are feasible with spectroscopic surveys. In reviewing the low-redshift content of the COSMOS field, we also note the existence of several dozen objects that appear resolved or partially resolved in the HST imaging, and are confirmed to be local (at distances of ~250Mpc or less) by their photometric or spectroscopic redshifts. This underlines the potential for future space-based surveys to reveal local populations of intrinsically faint galaxies through imaging alone.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/783/119
- Title:
- z~1 Ly{alpha} emitters. I. 135 candidates from GALEX
- Short Name:
- J/ApJ/783/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a flux-limited sample of 135 candidate z~1 Ly{alpha} emitters (LAEs) from Galaxy Evolution Explorer (GALEX) grism data using a new data cube search method. These LAEs have luminosities comparable to those at high redshifts and lie within a 7Gyr gap present in existing LAE samples. We use archival and newly obtained optical spectra to verify the UV redshifts of these LAEs. We use the combination of the GALEX UV spectra, optical spectra, and X-ray imaging data to estimate the active galactic nucleus (AGN) fraction and its dependence on Ly{alpha} luminosity. We remove the AGNs and compute the luminosity function (LF) from 60 z~1 LAE galaxies. We find that the best-fit LF implies a luminosity density increase by a factor of ~1.5 from z~0.3 to z~1 and ~20 from z~1 to z~2. We find a z~1 volumetric Ly{alpha} escape fraction of 0.7%+/-0.4%.
- ID:
- ivo://CDS.VizieR/J/ApJ/759/133
- Title:
- z=2.4 Ly{alpha} emitters in the 53W002 field
- Short Name:
- J/ApJ/759/133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our wide-field narrowband imaging of the field around the radio galaxy 53W002 at z=2.390 with Subaru/Suprime-Cam. A custom-made filter, NB413, centered at 4140{AA} with a width of 83{AA} is used to observe the 31'x24' area around the radio galaxy. We detected 204 Ly{alpha} emitters (LAEs) at z=2.4 with a rest-frame equivalent width larger than 25{AA} to the depth of 26 AB mag (in NB413). The entire LAE population in the 53W002 field has an average number density and distributions of equivalent width and size that are similar to those of other fields at z~2. We identify a significant high-density region (53W002F-HDR) that spreads over {approx}5'x4' near 53W002, where the LAE number density is nearly four times as large as the average of the entire field. Using the probability distribution function of density fluctuation, we evaluate the rareness probability of 53W002F-HDR to be 0.9^+2.4^_-0.62_%, which corresponds to a moderately rich structure. No notable environmental dependency at the comoving scale of 10Mpc is found for the distributions of the Ly{alpha} equivalent width and luminosity in the field. We also detected four Ly{alpha} blobs, one of which is newly discovered. They are all located in the rims of high-density regions. The biased location and unique morphologies in Ly{alpha} suggest that galaxy interaction plays a key role in their formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/123
- Title:
- z~4-7 Lyman break galaxies in Hubble deep fields
- Short Name:
- J/ApJ/821/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present clustering analysis results from 10381 Lyman break galaxies (LBGs) at z~4-7, identified in the Hubble legacy deep imaging and new complimentary large-area Subaru/Hyper Suprime-Cam data. We measure the angular correlation functions of these LBGs at z~4, 5, 6, and 7 and fit these measurements using halo occupation distribution (HOD) models that provide an estimate of halo masses, M_h_~(1-20)x10^11^M_{sun}_. Our Mh estimates agree with those obtained by previous clustering studies in a UV-magnitude versus Mh plane and allow us to calculate stellar-to-halo mass ratios (SHMRs) of LBGs. By comparison with the z~0 SHMR, we identify evolution of the SHMR from z~0 to z~4 and from z~4 to z~7 at the >98% confidence levels. The SHMR decreases by a factor of ~2 from z~0 to 4 and increases by a factor of ~4 from z~4 to 7 at the dark matter halo mass of M_h_~10^11^M_{sun}. We compare our SHMRs with results of a hydrodynamic simulation and a semianalytic model and find that these theoretical studies do not predict the SHMR increase from z~4 to 7. We obtain the baryon conversion efficiency (BCE) of LBGs at z~4 and find that the BCE increases with increasing dark matter halo mass. Finally, we compare our clustering+HOD estimates with results from abundance matching techniques and conclude that the Mh estimates of the clustering+HOD analyses agree with those of the simple abundance matching within a factor of 3, and that the agreement improves when using more sophisticated abundance matching techniques that include subhalos, incompleteness, and/or evolution in the star formation and stellar mass functions.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/158
- Title:
- z<0.5 PG quasars IR energy distributions
- Short Name:
- J/ApJ/854/158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interstellar medium is crucial to understanding the physics of active galaxies and the coevolution between supermassive black holes and their host galaxies. However, direct gas measurements are limited by sensitivity and other uncertainties. Dust provides an efficient indirect probe of the total gas. We apply this technique to a large sample of quasars, whose total gas content would be prohibitively expensive to measure. We present a comprehensive study of the full (1 to 500{mu}m) infrared spectral energy distributions of 87 redshift <0.5 quasars selected from the Palomar-Green sample, using photometric measurements from 2MASS, WISE, and Herschel, combined with Spitzer mid-infrared (5-40{mu}m) spectra. With a newly developed Bayesian Markov Chain Monte Carlo fitting method, we decompose various overlapping contributions to the integrated spectral energy distribution, including starlight, warm dust from the torus, and cooler dust on galaxy scales. This procedure yields a robust dust mass, which we use to infer the gas mass, using a gas-to-dust ratio constrained by the host galaxy stellar mass. Most (90%) quasar hosts have gas fractions similar to those of massive, star-forming galaxies, although a minority (10%) seem genuinely gas-deficient, resembling present-day massive early-type galaxies. This result indicates that "quasar mode" feedback does not occur or is ineffective in the host galaxies of low-redshift quasars. We also find that quasars can boost the interstellar radiation field and heat dust on galactic scales. This cautions against the common practice of using the far-infrared luminosity to estimate the host galaxy star formation rate.
- ID:
- ivo://CDS.VizieR/J/ApJ/826/114
- Title:
- z~3-6 protoclusters in the CFHTLS deep fields
- Short Name:
- J/ApJ/826/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of three protoclusters at z~3-4 with spectroscopic confirmation in the Canada-France-Hawaii Telescope Legacy Survey Deep Fields. In these fields, we investigate the large-scale projected sky distribution of z~3-6 Lyman-break galaxies and identify 21 protocluster candidates from regions that are overdense at more than 4{sigma} overdensity significance. Based on cosmological simulations, it is expected that more than 76% of these candidates will evolve into a galaxy cluster of at least a halo mass of 10^14^ M_{sun}_ at z=0. We perform follow-up spectroscopy for eight of the candidates using Subaru/FOCAS, Keck II/DEIMOS, and Gemini-N/GMOS. In total we target 462 dropout candidates and obtain 138 spectroscopic redshifts. We confirm three real protoclusters at z=3-4 with more than five members spectroscopically identified and find one to be an incidental overdense region by mere chance alignment. The other four candidate regions at z~5-6 require more spectroscopic follow-up in order to be conclusive. A z=3.67 protocluster, which has 11 spectroscopically confirmed members, shows a remarkable core-like structure composed of a central small region (<0.5 physical Mpc) and an outskirts region (~1.0 physical Mpc). The Ly{alpha} equivalent widths of members of the protocluster are significantly smaller than those of field galaxies at the same redshift, while there is no difference in the UV luminosity distributions. These results imply that some environmental effects start operating as early as at z~4 along with the growth of the protocluster structure. This study provides an important benchmark for our analysis of protoclusters in the upcoming Subaru/HSC imaging survey and its spectroscopic follow-up with the Subaru/PFS that will detect thousands of protoclusters up to z~6.
- ID:
- ivo://CDS.VizieR/J/ApJ/768/105
- Title:
- z~5 QSO luminosity function from SDSS Stripe 82
- Short Name:
- J/ApJ/768/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a measurement of the Type I quasar luminosity function at z=5 using a large sample of spectroscopically confirmed quasars selected from optical imaging data. We measure the bright end (M_1450_<-26) with Sloan Digital Sky Survey (SDSS) data covering ~6000deg^2^, then extend to lower luminosities (M_1450_<-24) with newly discovered, faint z~5 quasars selected from 235deg^2^ of deep, coadded imaging in the SDSS Stripe 82 region (the celestial equator in the Southern Galactic Cap). The faint sample includes 14 quasars with spectra obtained as ancillary science targets in the SDSS-III Baryon Oscillation Spectroscopic Survey, and 59 quasars observed at the MMT and Magellan telescopes. We construct a well-defined sample of 4.7<z<5.1 quasars that is highly complete, with 73 spectroscopic identifications out of 92 candidates. Our color selection method is also highly efficient: of the 73 spectra obtained, 71 are high-redshift quasars. These observations reach below the break in the luminosity function (M_1450_^*^~-27). The bright-end slope is steep ({beta}<~-4), with a constraint of {beta}<-3.1 at 95% confidence. The break luminosity appears to evolve strongly at high redshift, providing an explanation for the flattening of the bright-end slope reported previously. We find a factor of ~2 greater decrease in the number density of luminous quasars (M_1450_<-26) from z=5 to z=6 than from z=4 to z=5, suggesting a more rapid decline in quasar activity at high redshift than found in previous surveys. Our model for the quasar luminosity function predicts that quasars generate ~30% of the ionizing photons required to keep hydrogen in the universe ionized at z=5.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/24
- Title:
- z>4.5 QSOs with SDSS and WISE. I. Opt. spectra
- Short Name:
- J/ApJ/819/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-redshift quasars are important tracers of structure and evolution in the early universe. However, they are very rare and difficult to find when using color selection because of contamination from late-type dwarfs. High-redshift quasar surveys based on only optical colors suffer from incompleteness and low identification efficiency, especially at z>~4.5. We have developed a new method to select 4.7<~z>~5.4 quasars with both high efficiency and completeness by combining optical and mid-IR Wide-field Infrared Survey Explorer (WISE) photometric data, and are conducting a luminous z~5 quasar survey in the whole Sloan Digital Sky Survey (SDSS) footprint. We have spectroscopically observed 99 out of 110 candidates with z-band magnitudes brighter than 19.5, and 64 (64.6%) of them are quasars with redshifts of 4.4<~z<~5.5 and absolute magnitudes of -29<~M_1450_<~-26.4. In addition, we also observed 14 fainter candidates selected with the same criteria and identified 8 (57.1%) of them as quasars with 4.7<z<5.4. Among 72 newly identified quasars, 12 of them are at 5.2<z<5.7, which leads to an increase of ~36% of the number of known quasars at this redshift range. More importantly, our identifications doubled the number of quasars with M_1450_<-27.5 at z>4.5, which will set strong constraints on the bright end of the quasar luminosity function. We also expand our method to select quasars at z>~5.7. In this paper we report the discovery of four new luminous z>~5.7 quasars based on SDSS-WISE selection.
- ID:
- ivo://CDS.VizieR/J/AJ/155/131
- Title:
- z~5 quasar luminosity function from the CFHTLS
- Short Name:
- J/AJ/155/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a spectroscopic survey of z~5 quasars in the CFHT Legacy Survey (Cat. II/317). Using both optical color selection and a likelihood method, we select 97 candidates over an area of 105 deg^2^ to a limit of i_AB_<23.2, and 7 candidates in the range 23.2<i_AB_<23.7 over an area of 18.5 deg^2^. Spectroscopic observations for 43 candidates were obtained with Gemini, MMT, and Large Binocular Telescope, of which 37 are z>4 quasars. This sample extends measurements of the quasar luminosity function ~1.5 mag fainter than our previous work in Sloan Digital Sky Survey Stripe 82. The resulting luminosity function is in good agreement with our previous results, and suggests that the faint end slope is not steep. We perform a detailed examination of our survey completeness, particularly the impact of the Ly{alpha} emission assumed in our quasar spectral models, and find hints that the observed Ly{alpha} emission from faint z~5 quasars is weaker than for z~3 quasars at a similar luminosity. Our results strongly disfavor a significant contribution of faint quasars to the hydrogen-ionizing background at z=5.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/169
- Title:
- 3<z<5 quasar luminosity function in the COSMOS
- Short Name:
- J/ApJ/755/169
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the high-redshift quasar luminosity function (QLF) down to an apparent magnitude of I_AB_=25 in the Cosmic Evolution Survey (COSMOS). Careful analysis of the extensive COSMOS photometry and imaging data allows us to identify and remove stellar and low-redshift contaminants, enabling a selection that is nearly complete for type-1 quasars at the redshifts of interest. We find 155 likely quasars at z>3.1, 39 of which have prior spectroscopic confirmation. We present our sample in detail and use these confirmed and likely quasars to compute the rest-frame UV QLF in the redshift bins 3.1<z<3.5 and 3.5<z<5. The space density of faint quasars decreases by roughly a factor of four from z~3.2 to z~4, with faint-end slopes of {beta}~-1.7 at both redshifts. The decline in space density of faint optical quasars at z>3 is similar to what has been found for more luminous optical and X-ray quasars. We compare the rest-frame UV luminosity functions found here with the X-ray luminosity function at z>3, and find that they evolve similarly between z~3.2 and z~4; however, the different normalizations imply that roughly 75% of X-ray bright active galactic nuclei (AGNs) at z~3-4 are optically obscured. This fraction is higher than found at lower redshift and may imply that the obscured, type-2 fraction continues to increase with redshift at least to z~4. Finally, the implications of the results derived here for the contribution of quasars to cosmic reionization are discussed.
