- ID:
- ivo://CDS.VizieR/J/ApJ/770/138
- Title:
- Metallicities of Lyman limit systems and DLA
- Short Name:
- J/ApJ/770/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We assess the metal content of the cool (~10^4^K) circumgalactic medium (CGM) about galaxies at z<~1 using an H I-selected sample of 28 Lyman limit systems (LLS; defined here as absorbers with 16.2<~logN_HI_<~18.5) observed in absorption against background QSOs by the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The N_HI_ selection avoids metallicity biases inherent in many previous studies of the low-redshift CGM. We compare the column densities of weakly ionized metal species (e.g., O II, Si II, Mg II) to N_HI_ in the strongest H I component of each absorber. We find that the metallicity distribution of the LLS (and hence the cool CGM) is bimodal with metal-poor and metal-rich branches peaking at [X/H]=~-1.6 and -0.3 (or about 2.5% and 50% solar metallicities). The cool CGM probed by these LLS is predominantly ionized. The metal-rich branch of the population likely traces winds, recycled outflows, and tidally stripped gas; the metal-poor branch has properties consistent with cold accretion streams thought to be a major source of fresh gas for star forming galaxies. Both branches have a nearly equal number of absorbers. Our results thus demonstrate there is a significant mass of previously undiscovered cold metal-poor gas and confirm the presence of metal enriched gas in the CGM of z<~1 galaxies.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/819/73
- Title:
- Metallicity evolution of COSMOS BCD sample
- Short Name:
- J/ApJ/819/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present oxygen abundance measurements for 74 blue compact dwarf (BCD) galaxies in the redshift range of [0.2, 0.5] using the strong-line method. The spectra of these objects are taken using Hectospec on the Multiple Mirror Telescope. More than half of these BCDs had dust attenuation corrected using the Balmer decrement method. For comparison, we also selected a sample of 2023 local BCDs from the Sloan Digital Sky Survey (SDSS) database. Based on the local and intermediate-z BCD samples, we investigated the cosmic evolution of the metallicity, star formation rate (SFR), and D_n_(4000) index. Compared with local BCDs, the intermediate-z BCDs had a systematically higher R23 ratio but a similar O32 ratio. Interestingly, no significant deviation in the mass-metallicity (MZ) relation was found between the intermediate-z and local BCDs. Besides the metallicity, the intermediate-z BCDs also exhibited an SFR distribution that was consistent with local BCDs, suggesting a weak dependence on redshift. The intermediate-z BCDs seemed to be younger than the local BCDs with lower D_n_(4000) index values. The insignificant deviation in the mass-metallicity and mass-SFR relations between intermediate-z and local BCDs indicates that the relations between the global parameters of low-mass compact galaxies may be universal. These results from low-mass compact galaxies could be used to place important observational constraints on galaxy formation and evolution models.
- ID:
- ivo://CDS.VizieR/J/ApJ/834/186
- Title:
- Metallicity of MPA-JHU SDSS-DR7 dwarf galaxies
- Short Name:
- J/ApJ/834/186
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study how the cosmic environment affects galaxy evolution in the universe by comparing the metallicities of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the fluxes of emission lines, particularly those of the forbidden [OIII] and [SII] transitions, provide estimates of a region's electron temperature and number density. From these two quantities and the emission line fluxes [OII]{lambda}3727, [OIII]{lambda}4363, and [OIII]{lambda}{lambda}4959,5007, we estimate the abundance of oxygen with the direct T_e_ method. We estimate the metallicity of 42 blue, star-forming void dwarf galaxies and 89 blue, star-forming dwarf galaxies in more dense regions using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, as reprocessed in the MPA-JHU value-added catalog. We find very little difference between the two sets of galaxies, indicating little influence from the large-scale environment on their chemical evolution. Of particular interest are a number of extremely metal-poor dwarf galaxies that are less prevalent in voids than in the denser regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/685/904
- Title:
- Metal-rich dwarf galaxies from SDSS-DR4
- Short Name:
- J/ApJ/685/904
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified a sample of 41 low-mass high-oxygen abundance outliers from the mass-metallicity relation of star-forming galaxies measured by Tremonti et al. (2004ApJ...613..898T). These galaxies, which have 8.6<12+log(O/H)<9.3 over a range of -14.4>M_B_>-19.1 and 7.4<log(M_*_/M_{sun}_)<10, are surprisingly nonpathological. They have typical specific star formation rates, are fairly isolated, and, with few exceptions, have no obvious companions. Morphologically, they are similar to dwarf spheroidal or dwarf elliptical galaxies. We predict that their observed high oxygen abundances are due to relatively low gas fractions, concluding that these are transitional dwarf galaxies nearing the end of their star formation activity.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/37
- Title:
- Metals in SDSS QSOs. I. 1.5<z<4.5 CIV absorbers
- Short Name:
- J/ApJ/763/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have vastly increased the CIV statistics at intermediate redshift by surveying the thousands of quasars in the Sloan Digital Sky Survey (SDSS) Data-Release 7. We visually verified over 16000 CIV systems with 1.46<z<4.55 - a sample size that renders Poisson error negligible. Detailed Monte Carlo simulations show that we are approximately 50% complete down to rest equivalent widths W_r_{approx}0.6{AA}. We analyzed the sample as a whole and in 10 small redshift bins with approximately 1500 doublets each. The equivalent width frequency distributions f(W_r_) were well modeled by an exponential, with little evolution in shape. In contrast with previous studies that modeled the frequency distribution as a single power law, the fitted exponential gives a finite mass density for the CIV ions. The comoving line density dN_CIV_/dX evolved smoothly with redshift, increasing by a factor of 2.37+/-0.09 from z=4.55-1.96, then plateauing at dN_CIV_/dX~0.34 for z=1.96-1.46. Comparing our SDSS sample with z<1 (ultraviolet) and z>5 (infrared) surveys, we see an approximately 10-fold increase in dN_CIV_/dX over z{approx}6->0, for W_r_>=0.6{AA}. This suggests a monotonic and significant increase in the enrichment of gas outside galaxies over the 12Gyr lifetime of the universe.
- ID:
- ivo://CDS.VizieR/J/ApJ/748/131
- Title:
- MgII absorbers in SDSS-DR7 quasar catalog
- Short Name:
- J/ApJ/748/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A few percent of quasars show strong associated Mg II absorption, with velocities (v_off_) lying within a few thousand km/s from the quasar systemic redshift. These associated absorption line (AAL) systems are usually interpreted as absorbers that are either intrinsic to the quasar and its host, or arising from external galaxies clustering around the quasar. Using composite spectra of ~1800 Mg II AAL quasars selected from SDSS DR7 at 0.4<~z<~2, we show that quasars with AALs with v_off_<1500km/s have a prominent excess in [OII]{lambda}3727 emission (detected at >7{sigma}) at rest relative to the quasar host, compared to unabsorbed quasars. We interpret this [OII] excess as due to enhanced star formation in the quasar host. Our results suggest that a significant fraction of AALs with v_off_<1500km/s are physically associated with the quasar and its host. AAL quasars also have dust reddening lying between normal quasars and the so-called dust-reddened quasars. We suggest that the unique properties of AAL quasars can be explained if they are the transitional population from heavily dust-reddened quasars to normal quasars in the formation process of quasars and their hosts. This scenario predicts a larger fraction of young bulges, disturbed morphologies, and interactions of AAL quasar hosts compared to normal quasars. The intrinsic link between associated absorbers and quasar hosts opens a new window to probe massive galaxy formation and galactic-scale feedback processes, and provides a crucial test of the evolutionary picture of quasars.
- ID:
- ivo://CDS.VizieR/J/ApJ/779/161
- Title:
- MgII absorbers in 0.4<z<2.3 SDSS QSOs
- Short Name:
- J/ApJ/779/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed an analysis of over 34000 Mg II doublets at 0.36<z<2.29 in Sloan Digital Sky Survey (SDSS) Data Release 7 quasar spectra; the catalog, advanced data products, and tools for analysis are publicly available. The catalog was divided into 14 small redshift bins with roughly 2500 doublets in each and from Monte Carlo simulations, we estimate 50% completeness at rest equivalent width W_r_{approx}0.8{AA}. The equivalent width frequency distribution is described well by an exponential model at all redshifts, and the distribution becomes flatter with increasing redshift, i.e., there are more strong systems relative to weak ones. Direct comparison with previous SDSS Mg II surveys reveals that we recover at least 70% of the doublets in these other catalogs, in addition to detecting thousands of new systems. We discuss how these surveys came by their different results, which qualitatively agree but because of the very small uncertainties, differ by a statistically significant amount. The estimated physical cross section of Mg II-absorbing galaxy halos increased approximately threefold from z=0.4 to z=2.3, while the W_r_>=1{AA} absorber line density, dN_MgII_/dX, grew by roughly 45%. Finally, we explore the different evolution of various absorber populations --damped Ly{alpha} absorbers, Lyman limit systems, strong C IV absorbers, and strong and weaker MgII systems -- across cosmic time (0<z<6).
- ID:
- ivo://CDS.VizieR/J/ApJ/724/L176
- Title:
- MgII absorbing gas around galaxies
- Short Name:
- J/ApJ/724/L176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the connections between ongoing star formation, galaxy mass, and extended halo gas, in order to distinguish between starburst-driven outflows and infalling clouds that produce the majority of observed MgII absorbers at large galactic radii (>~10h^-1^kpc) and to gain insights into halo gas contents around galaxies. We present new measurements of total stellar mass (M_star_), H{alpha} emission line strength (EW(H{alpha})), and specific star formation rate (sSFR) for the 94 galaxies described by Chen et al.'s 2010 paper (Cat. J/ApJ/714/1521).
- ID:
- ivo://CDS.VizieR/J/ApJ/754/38
- Title:
- MgII absorption systems for Flat-Spectrum Radio QSOs
- Short Name:
- J/ApJ/754/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The conventional wisdom that the rate of incidence of MgII absorption systems, dN/dz (excluding "associated systems" having a velocity {beta}c relative to the active galactic nucleus (AGN) of less than ~5000km/s), is totally independent of the background AGNs has been challenged by a recent finding that dN/dz for strong MgII absorption systems toward distant blazars is 2.2+/-^0.8^_0.6_ times the value known for normal optically selected quasars (QSOs). This has led to the suggestion that a significant fraction of even the absorption systems with {beta} as high as ~0.1 may have been ejected by the relativistic jets in the blazars, which are expected to be pointed close to our direction. Here, we investigate this scenario using a large sample of 115 flat-spectrum radio-loud quasars (FSRQs) that also possess powerful jets, but are only weakly polarized. We show, for the first time, that dN/dz toward FSRQs is, on the whole, quite similar to that known for QSOs and that the comparative excess of strong MgII absorption systems seen toward blazars is mainly confined to {beta}<0.15. The excess relative to FSRQs probably results from a likely closer alignment of blazar jets with our direction; hence, any gas clouds accelerated by them are more likely to be on the line of sight to the active quasar nucleus.
- ID:
- ivo://CDS.VizieR/J/ApJ/890/132
- Title:
- MgII abs. toward SDSS QSOs with rotation measures
- Short Name:
- J/ApJ/890/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (RRM) for quasar sightlines with intervening MgII absorbers. Based on a large sample of 1132 quasars, we have computed RRM distributions broadening using median absolute deviation from the mean ({sigma}_rrm_^md^), and found it to be 17.1+/-0.7rad/m^2^ for 352 sightlines having MgII intervening absorbers in comparison to its value of 15.1+/-0.6rad/m^2^ for 780 sightlines without such absorbers, resulting in an excess broadening ({sigma}_rrm_^ex^) of 8.0+/-1.9rad:m^2^ among these two subsamples. This value of {sigma}_rrm_^ex^, has allowed us to constrain the average strength of magnetic field (rest frame) in high-redshift galaxies responsible for these Mg II absorbers, to be ~1.3+/-0.3{mu}G at a median redshift of 0.92. This estimate of magnetic field is consistent with the reported estimate in earlier studies based on radio-infrared correlation and energy equipartition for galaxies in the local universe. A similar analysis on subsample split based on the radio spectral index, {alpha} (with F_{nu}_{propto}{nu}^{alpha}^), for flat ({alpha}>=-0.3; 315 sources) and steep ({alpha}<=-0.7; 476 sources) spectrum sources shows a significant {sigma}_rrm_^ex^ (at 3.5{sigma} level) for the former and absent in the latter. An anticorrelation found between the {sigma}_rrm_^md^ and percentage polarization (p) with a similar Pearson correlation of -0.62 and -0.87 for subsamples with and without MgII, respectively, suggests the main contribution for decrements in the p value to be intrinsic to the local environment of quasars.
