skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Quasars Probing Galaxies. I. Signatures of Gas Accretion at Redshift z ≈ 0.2

Abstract

We describe the kinematics of circumgalactic gas near the galactic plane, combining new measurements of galaxy rotation curves and spectroscopy of background quasars. The sightlines pass within 19–93 kpc of the target galaxy and generally detect Mg ii absorption. The Mg ii Doppler shifts have the same sign as the galactic rotation, so the cold gas co-rotates with the galaxy. Because the absorption spans a broader velocity range than disk rotation can explain, we explore simple models for the circumgalactic kinematics. Gas spiraling inwards (near the disk plane) offers a successful description of the observations. An appendix describes the addition of tangential and radial gas flows and illustrates how the sign of the disk inclination produces testable differences in the projected line-of-sight velocity range. This inflow interpretation implies that cold flow disks remain common down to redshift z ≈ 0.2 and prolong star formation by supplying gas to the disk.

Authors:
;  [1];  [2];  [3]
  1. Department of Physics, University of California, Santa Barbara, CA 93106 (United States)
  2. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122 (Australia)
  3. Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States)
Publication Date:
OSTI Identifier:
22663903
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; DOPPLER EFFECT; EVOLUTION; GALAXIES; GAS FLOW; QUASARS; RED SHIFT; ROTATION; SPECTROSCOPY; STARS; VELOCITY

Citation Formats

Ho, Stephanie H., Martin, Crystal L., Kacprzak, Glenn G., and Churchill, Christopher W., E-mail: shho@physics.ucsb.edu, E-mail: cmartin@physics.ucsb.edu. Quasars Probing Galaxies. I. Signatures of Gas Accretion at Redshift z ≈ 0.2. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/267.
Ho, Stephanie H., Martin, Crystal L., Kacprzak, Glenn G., & Churchill, Christopher W., E-mail: shho@physics.ucsb.edu, E-mail: cmartin@physics.ucsb.edu. Quasars Probing Galaxies. I. Signatures of Gas Accretion at Redshift z ≈ 0.2. United States. doi:10.3847/1538-4357/835/2/267.
Ho, Stephanie H., Martin, Crystal L., Kacprzak, Glenn G., and Churchill, Christopher W., E-mail: shho@physics.ucsb.edu, E-mail: cmartin@physics.ucsb.edu. Wed . "Quasars Probing Galaxies. I. Signatures of Gas Accretion at Redshift z ≈ 0.2". United States. doi:10.3847/1538-4357/835/2/267.
@article{osti_22663903,
title = {Quasars Probing Galaxies. I. Signatures of Gas Accretion at Redshift z ≈ 0.2},
author = {Ho, Stephanie H. and Martin, Crystal L. and Kacprzak, Glenn G. and Churchill, Christopher W., E-mail: shho@physics.ucsb.edu, E-mail: cmartin@physics.ucsb.edu},
abstractNote = {We describe the kinematics of circumgalactic gas near the galactic plane, combining new measurements of galaxy rotation curves and spectroscopy of background quasars. The sightlines pass within 19–93 kpc of the target galaxy and generally detect Mg ii absorption. The Mg ii Doppler shifts have the same sign as the galactic rotation, so the cold gas co-rotates with the galaxy. Because the absorption spans a broader velocity range than disk rotation can explain, we explore simple models for the circumgalactic kinematics. Gas spiraling inwards (near the disk plane) offers a successful description of the observations. An appendix describes the addition of tangential and radial gas flows and illustrates how the sign of the disk inclination produces testable differences in the projected line-of-sight velocity range. This inflow interpretation implies that cold flow disks remain common down to redshift z ≈ 0.2 and prolong star formation by supplying gas to the disk.},
doi = {10.3847/1538-4357/835/2/267},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}
  • We characterize the physical properties of the cool T  ∼ 10{sup 4} K circumgalactic medium (CGM) surrounding z  ∼ 2–3 quasar host galaxies, which are predicted to evolve into present-day massive ellipticals. Using a statistical sample of 14 quasar pairs with projected separation <300 kpc and spectra of high dispersion and high signal-to-noise ratio, we find extreme kinematics with low metal ion lines typically spanning ≈500 km s{sup −1}, exceeding any previously studied galactic population. The CGM is significantly enriched, even beyond the virial radius, with a median metallicity [M/H] ≈ −0.6. The α /Fe abundance ratio is enhanced, suggesting that halo gas ismore » primarily enriched by core-collapse supernovae. The projected cool gas mass within the virial radius is estimated to be 1.9 × 10{sup 11} M {sub ⊙} ( R {sub ⊥}/160 kpc){sup 2}, accounting for ≈1/3 of the baryonic budget of the galaxy halo. The ionization state of CGM gas increases with projected distance from the foreground quasars, contrary to expectation if the quasar dominates the ionizing radiation flux. However, we also found peculiarities not exhibited in the CGM of other galaxy populations. In one absorption system, we may be detecting unresolved fluorescent Ly α emission, and another system shows strong N v lines. Taken together, these anomalies suggest that transverse sightlines are—at least in some cases—possibly illuminated. We also discovered a peculiar case where detection of the C ii fine-structure line implies an electron density >100 cm{sup −3} and sub-parsec-scale gas clumps.« less
  • With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We use a sample of 650 projected quasar pairs to study the H I Lyα absorption transverse to luminous, z ∼ 2 quasars at proper separations of 30 kpc < R < 1 Mpc. In contrast to measurements along the line-of-sight, regions transverse to quasars exhibit enhanced H I Lyα absorption and a larger variance than the ambient intergalactic medium, with increasing absorption and variance toward smaller scales. Analysis of composite spectra reveals excess absorption characterized bymore » a Lyα equivalent width profile W = 2.3 Å (R /100 kpc){sup –0.46}. We also observe a high (≅ 60%) covering factor of strong, optically thick H I absorbers (H I column N{sub H{sub I}}>10{sup 17.3} cm{sup -2}) at separations R < 200 kpc, which decreases to ∼20% at R ≅ 1 Mpc, but still represents a significant excess over the cosmic average. This excess of optically thick absorption can be described by a quasar-absorber cross-correlation function ξ{sub QA}(r) = (r/r{sub 0}){sup γ} with a large correlation length r{sub 0} = 12.5{sup +2.7}{sub -1.4} h{sup -1} Mpc (comoving) and γ=1.68{sup +0.14}{sub -0.30}. The H I absorption measured around quasars exceeds that of any previously studied population, consistent with quasars being hosted by massive dark matter halos M{sub halo} ≈ 10{sup 12.5} M{sub ☉} at z ∼ 2.5. The environments of these massive halos are highly biased toward producing optically thick gas, and may even dominate the cosmic abundance of Lyman limit systems and hence the intergalactic opacity to ionizing photons at z ∼ 2.5. The anisotropic absorption around quasars implies the transverse direction is much less likely to be illuminated by ionizing radiation than the line-of-sight.« less
  • We survey the incidence and absorption strength of the metal-line transitions C II 1334 and C IV 1548 from the circumgalactic medium (CGM) surrounding z ∼ 2 quasars, which act as signposts for massive dark matter halos M {sub halo} ≈ 10{sup 12.5} M {sub ☉}. On scales of the virial radius (r {sub vir} ≈ 160 kpc), we measure a high covering fraction f{sub C} = 0.73 ± 0.10 to strong C II 1334 absorption (rest equivalent width W {sub 1334} ≥ 0.2 Å), implying a massive reservoir of cool (T ∼ 10{sup 4} K) metal enriched gas. Wemore » conservatively estimate a metal mass exceeding 10{sup 8} M {sub ☉}. We propose that these metals trace enrichment of the incipient intragroup/intracluster medium that these halos eventually inhabit. This cool CGM around quasars is the pinnacle among galaxies observed at all epochs, as regards covering the fraction and average equivalent width of H I Lyα and low-ion metal absorption. We argue that the properties of this cool CGM primarily reflect the halo mass, and that other factors such as feedback, star-formation rate, and accretion from the intergalactic medium are secondary. We further estimate that the CGM of massive, z ∼ 2 galaxies accounts for the majority of strong Mg II absorption along random quasar sightlines. Last, we detect an excess of strong C IV 1548 absorption (W {sub 1548} ≥ 0.3 Å) over random incidence to the 1 Mpc physical impact parameter and measure the quasar-C IV cross-correlation function: ξ{sub C} {sub IV-Q}(r)=(r/r{sub 0}){sup −γ} with r{sub 0}=7.5{sub −1.4}{sup +2.8} h{sup −1} Mpc and γ=1.7{sub −0.2}{sup +0.1}. Consistent with previous work on larger scales, we infer that this highly ionized C IV gas traces massive (10{sup 12} M {sub ☉}) halos.« less
  • We present an analysis of two O VI absorbers at redshift z {sub abs} = 0.227, which were detected in the spectra of two closely spaced QSO sightlines (Q 0107–025A and B) and observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope. At the same redshift, the presence of a single bright (∼1.2L {sub *}) galaxy at an impact parameter of ∼200 kpc (proper) from both the sightlines was reported by Crighton et al. Using detailed photoionization models, we show that the high ionization phases of both the O VI absorbers have similar ionization conditions (e.g., log Umore » ∼ –1.1 to –0.9), chemical enrichment (e.g., log Z ∼ –1.4 to –1.0), total hydrogen column density (e.g., log N {sub H}(cm{sup –2}) ∼ 19.6 – 19.7), and line of sight thickness (e.g., l {sub los} ∼ 600-800 kpc). Therefore we speculate that the O VI absorbers are tracing different parts of same large-scale structure, presumably the circumgalactic medium (CGM) of the identified galaxy. Using sizes along and transverse to the line of sight, we estimate the size of the CGM to be R ∼ 330 kpc. The baryonic mass associated with this large CGM as traced by O VI absorption is ∼1.2 × 10{sup 11} M {sub ☉}. A low ionization phase is detected in one of the O VI systems with near-solar metallicity (log Z = 0.20 ± 0.20) and parsec scale size (l {sub los} ∼ 6 pc), possibly tracing the neutral phase of a high-velocity cloud embedded within the CGM.« less
  • We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9. This is the initial result from the Subaru High- z Exploration of Low-Luminosity Quasars project, which exploits the exquisite multiband imaging data produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The candidate selection is performed by combining several photometric approaches including a Bayesian probabilistic algorithm to reject stars and dwarfs. The spectroscopic identification was carried out with the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg{sup 2} of the survey footprint. The success rate of our photometric selectionmore » is quite high, approaching 100% at the brighter magnitudes (z {sub AB} < 23.5 mag). Our selection also recovered all the known high- z quasars on the HSC images. Among the 15 discovered objects, six are likely quasars, while the other six with interstellar absorption lines and in some cases narrow emission lines are likely bright Lyman-break galaxies. The remaining three objects have weak continua and very strong and narrow Ly α lines, which may be excited by ultraviolet light from both young stars and quasars. These results indicate that we are starting to see the steep rise of the luminosity function of z ≥ 6 galaxies, compared with that of quasars, at magnitudes fainter than M {sub 1450} ∼ −22 mag or z {sub AB} ∼ 24 mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing.« less