Search

Start Over Validation Level 2 Capability Type Simple Cone Search
18061. z>4.5 QSOs with SDSS and WISE. I. Opt. spectra
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.
18062. z>1.5 QSO VLT-XSHOOTER spectra
ID:
ivo://CDS.VizieR/J/A+A/616/A158
Title:
z>1.5 QSO VLT-XSHOOTER spectra
Short Name:
J/A+A/616/A158
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study a sample of 17 z>1.5 absorbers selected based on the presence of strong neutral carbon (CI) absorption lines in Sloan Digital Sky Survey (SDSS) spectra and observed with the European Southern Observatory Very Large Telescope (ESO-VLT) spectrograph X-shooter. We derive metallicities, depletion onto dust, and extinction by dust, and analyse the absorption from MgII, MgI, CaII, and NaI that are redshifted into the near infrared wavelength range. We show that most of these CI absorbers have high metallicity and dust content. We detect nine CaII absorptions with W(CaI 3934)>0.23{AA} out of 14 systems where we have appropriate wavelength coverage. The observed equivalent widths are similar to what has been measured in other lower redshift surveys of CaII systems. We detect ten NaI absorptions in the 11 systems where we could observe this absorption. The median equivalent width (W(NaI 5891)=0.68{AA}) is larger than what is observed in local clouds with similar HI column densities but also in z<0.7 CaII systems detected in the SDSS. The systematic presence of NaI absorption in these CI systems strongly suggests that the gas is neutral and cold, maybe part of the diffuse molecular gas in the interstellar medium (ISM) of high-redshift galaxies. Most of the systems (12 out of 17) have W(MgII 2796)>2.5{AA} and six of them have logN(HI)<20.3, with the extreme case of J1341+1852 that has log N(HI)=18.18. The MgII absorptions are spread over more than {Delta}v~400km/s for half of the systems; three absorbers have {Delta}v>500km/s. The kinematics are strongly perturbed for most of these systems, which indicates that these systems probably do not arise in quiet disks and must be close to regions with intense star-formation activity and/or are part of interacting objects. All this suggests that a large fraction of the cold gas at high redshift arises in disturbed environments.
18063. z~5 quasar luminosity function from the CFHTLS
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.
18064. 3<z<5 quasar luminosity function in the COSMOS
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.
18065. z~0.8 quiescent galaxy kinematics from LEGA-C
ID:
ivo://CDS.VizieR/J/ApJ/858/60
Title:
z~0.8 quiescent galaxy kinematics from LEGA-C
Short Name:
J/ApJ/858/60
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present stellar rotation curves and velocity dispersion profiles for 104 quiescent galaxies at z=0.6-1 from the Large Early Galaxy Astrophysics Census (LEGA-C) spectroscopic survey. Rotation is typically probed across 10-20kpc, or to an average of 2.7Re. Combined with central stellar velocity dispersions ({sigma}0) this provides the first determination of the dynamical state of a sample selected by a lack of star formation activity at large lookback time. The most massive galaxies (M_*_>2x10^11^M_{sun}_) generally show no or little rotation measured at 5 kpc (|V_5_|/{sigma}_0_<0.2 in eight of ten cases), while ~64% of less massive galaxies show significant rotation. This is reminiscent of local fast- and slow- rotating ellipticals and implies that low- and high-redshift quiescent galaxies have qualitatively similar dynamical structures. We compare |V_5_|/{sigma}_0_ distributions at z~0.8 and the present day by re-binning and smoothing the kinematic maps of 91 low-redshift quiescent galaxies from the Calar Alto Legacy Integral Field Area (CALIFA) survey and find evidence for a decrease in rotational support since z~1. This result is especially strong when galaxies are compared at fixed velocity dispersion; if velocity dispersion does not evolve for individual galaxies then the rotational velocity at 5kpc was an average of 94+/-22% higher in z~0.8 quiescent galaxies than today. Considering that the number of quiescent galaxies grows with time and that new additions to the population descend from rotationally supported star-forming galaxies, our results imply that quiescent galaxies must lose angular momentum between z~1 and the present, presumably through dissipationless merging, and/or that the mechanism that transforms star-forming galaxies also reduces their rotational support.
18066. Zr, Ba, La, and Eu abundances in 19 open clusters
ID:
ivo://CDS.VizieR/J/AJ/145/107
Title:
Zr, Ba, La, and Eu abundances in 19 open clusters
Short Name:
J/AJ/145/107
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an analysis of the s-process elements Zr, Ba, and La and the r-process element Eu in a sample of 50 stars in 19 open clusters. Stellar abundances of each element are based on measures of a minimum of two lines per species via both equivalent width and spectrum synthesis techniques. We investigate cluster mean neutron-capture abundance trends as a function of cluster age and location in the Milky Way disk and compare them to results found in other studies in the literature. We find a statistically significant trend of increasing cluster [Ba/Fe] as a function of decreasing cluster age, in agreement with recent findings for other open cluster samples, supporting the increased importance of low-mass asymptotic giant branch stars to the generation of s-process elements. However, the other s-process elements, [La/Fe] and [Zr/Fe], do not show similar dependences, in contrast to theoretical expectations and the limited observational data from other studies. Conversely, cluster [Eu/Fe] ratios show a slight increase with increasing cluster age, although with marginal statistical significance. Ratios of [s/r]-process abundances, [Ba/Eu] and [La/Eu], however, show more clearly the increasing efficiency of s-process relative to r-process enrichment in open cluster chemical evolution, with significant increases among younger clusters. Last, cluster neutron-capture element abundances appear to be independent of Galactocentric distance. We conclude that a homogeneous analysis of a larger sample of open clusters is needed to resolve the apparent discrepant conclusions between different studies regarding s-process element abundance trends with age to better inform models of galactic chemical evolution.
18067. z<0.4 sources from Chandra/SDSS
ID:
ivo://CDS.VizieR/J/ApJ/778/188
Title:
z<0.4 sources from Chandra/SDSS
Short Name:
J/ApJ/778/188
Date:
21 Oct 2021
Publisher:
CDS
Description:
Striking similarities have been seen between accretion signatures of Galactic X-ray binary (XRB) systems and active galactic nuclei (AGNs). XRB spectral states show a V-shaped correlation between X-ray spectral hardness and Eddington ratio as they vary, and some AGN samples reveal a similar trend, implying analogous processes at vastly larger masses and timescales. To further investigate the analogies, we have matched 617 sources from the Chandra Source Catalog (CSC) to Sloan Digital Sky Survey (SDSS) spectroscopy, and uniformly measured both X-ray and optical spectral characteristics across a broad range of AGN and galaxy types. We provide useful tabulations of X-ray spectral slope for broad- and narrow-line AGNs, star-forming and passive galaxies, and composite systems, also updating relationships between optical (H{alpha} and [OIII]) line emission and X-ray luminosity. We further fit broadband spectral energy distributions with a variety of templates to estimate bolometric luminosity. Our results confirm a significant trend in AGNs between X-ray spectral hardness and Eddington ratio expressed in X-ray luminosity, albeit with significant dispersion. The trend is not significant when expressed in the full bolometric or template-estimated AGN luminosity. We also confirm a relationship between the X-ray/optical spectral slope {alpha}_ox_ and Eddington ratio, but it may not follow the trend predicted by analogy with XRB accretion states.
18068. z~1 star-forming galaxies catalog
ID:
ivo://CDS.VizieR/J/MNRAS/503/1753
Title:
z~1 star-forming galaxies catalog
Short Name:
J/MNRAS/503/1753
Date:
02 Feb 2022 09:53:58
Publisher:
CDS
Description:
We investigate the shape of the rotation curves (RCs) of z~1 star-forming galaxies (SFGs) and compare them with local SFGs. For this purpose, we have used 344 galaxies from the K-band Multi-Object Spectrograph (KMOS) for Redshift One Spectroscopic Survey (KROSS). This sample covers the redshift range 0.57<=z<=1.04, the effective radii 0.69<=R_e_[kpc]<=7.76, and the stellar masses 8.7<=log(M_*_[M_{sun}_])<=11.32. Using ^3D^BAROLO, we extract the H {alpha} kinematic maps and corresponding RCs. The main advantage of ^3D^BAROLO is that it incorporates the beam smearing in the 3D observational space, which provide us with the intrinsic rotation velocity even in the low spatial resolution data. We have corrected the RCs for pressure support, which seems to be a more dominant effect than beam smearing in high-z galaxies. Only a combination of the three techniques (3D-kinematic modelling + 3D-beam smearing correction + pressure gradient correction) yields the intrinsic RC of an individual galaxy. Further, we present the co-added and binned RCs constructed out of 256 high-quality objects. We do not see any change in the shape of RCs with respect to the local SFGs. Moreover, we notice a significant evolution in the stellar-disc length (R_D_) of the galaxies as a function of their circular velocity. Therefore, we conclude that the stellar disc of SFGs evolves over cosmic time (from z~1) while the total mass stays constant (within ~20kpc).
18069. z~3.3 star-forming galaxies NIR spectra
ID:
ivo://CDS.VizieR/J/ApJ/822/42
Title:
z~3.3 star-forming galaxies NIR spectra
Short Name:
J/ApJ/822/42
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the relationship between stellar mass, star formation rate (SFR), ionization state, and gas-phase metallicity for a sample of 41 normal star-forming galaxies at 3<~z<~3.7. The gas-phase oxygen abundance, ionization parameter, and electron density of ionized gas are derived from rest-frame optical strong emission lines measured on near-infrared spectra obtained with Keck/Multi-Object Spectrograph for Infra-Red Exploration. We remove the effect of these strong emission lines in the broadband fluxes to compute stellar masses via spectral energy distribution fitting, while the SFR is derived from the dust-corrected ultraviolet luminosity. The ionization parameter is weakly correlated with the specific SFR, but otherwise the ionization parameter and electron density do not correlate with other global galaxy properties such as stellar mass, SFR, and metallicity. The mass-metallicity relation (MZR) at z~3.3 shows lower metallicity by ~0.7dex than that at z=0 at the same stellar mass. Our sample shows an offset by ~0.3dex from the locally defined mass-metallicity-SFR relation, indicating that simply extrapolating such a relation to higher redshift may predict an incorrect evolution of MZR. Furthermore, within the uncertainties we find no SFR-metallicity correlation, suggesting a less important role of SFR in controlling the metallicity at high redshift. We finally investigate the redshift evolution of the MZR by using the model by Lilly et al. (2013ApJ...772..119L), finding that the observed evolution from z=0 to z~3.3 can be accounted for by the model assuming a weak redshift evolution of the star formation efficiency.
18070. z>4 submillimeter galaxies
ID:
ivo://CDS.VizieR/J/ApJ/712/942
Title:
z>4 submillimeter galaxies
Short Name:
J/ApJ/712/942
Date:
21 Oct 2021
Publisher:
CDS
Description:
The existence of submillimeter-selected galaxies (SMGs) at redshifts z>4 has recently been confirmed. Simultaneously using all the available data from UV to radio, we have modeled the spectral energy distributions of the six known spectroscopically confirmed SMGs at z>4. We find that their star formation rates (average ~2500M_{sun}_/yr), stellar (~3.6x10^11^M_{sun}_) and dust (~6.7x10^8^M_{sun}_) masses, extinction (A_V_~2.2mag), and gas-to-dust ratios (~60) are within the ranges for 1.7<z<3.6 SMGs. Our analysis suggests that infrared-to-radio luminosity ratios of SMGs do not change up to redshift ~5 and are lower by a factor of ~2.1 than the value corresponding to the local IR-radio correlation. However, we also find dissimilarities between z>4 and lower-redshift SMGs. Those at z>4 tend to be among the most star-forming, least massive, and hottest (~60K) SMGs and exhibit the highest fraction of stellar mass formed in the ongoing starburst (~45%).

Limit your search

more »

more »

more »

more »

more »

more »