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— Examples of H I maps and ∆V 90 calculations for four of the THINGS galaxies: NGC 925, NGC 3077, NGC 2841, and NGC 2903. The top row of panels shows the H I column density distributions. The greyscales range from log N HI = 19.8 to 21.8. The bottom row of panels shows the distribution of ∆V 90 over the region of the galaxies for which the H I column density exceeds the DLA limit of 2 × 10 20 cm −2 . The full range of the greyscale is 0 to 100 km s −1 . The black regions are those where ∆V 90 exceeds 100 km s −1 . The black spots that can be seen for example in the northern and southern outskirts of NGC 2903 are due to noisy spectra, where the ∆V 90 calculation is unreliable. In NGC 2841, the extended dark regions in the ∆V 90 map are associated with high N HI regions and indicate true high values of ∆V 90 .
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We demonstrate in this paper that the velocity widths of the neutral gas in damped Lyα (DLA) systems are inconsistent with these systems originating in gas disks of galaxies, similar to those seen in the local universe. We examine the gas kinematics of local galaxies using the high-quality H I 21 cm data from the H I Nearby Galaxies Survey and make...
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... principle, this method could cause an underestimation of ∆V 90 , but tests with syn- thetic spectra show that this effect is minimal. Figure 2 shows four examples of the ∆V 90 calculations for the THINGS galaxies. We choose to show the nearly face-on barred spiral NGC 925, the M81-group member NGC 3077 know for its extended tidal HI, the isolated nearly edge-on early-type spiral NGC 2841, and the barred nuclear starburst galaxy NGC 2903. ...
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Citations
... In the local Universe, extended H i disks are typically seen around galaxies at scales of up to a few kiloparsecs 23 , with a small population of disk galaxies showing extended H i disks out to tens of kiloparsecs 24 . It is also found that the H i kinematics in local H i disk galaxies 25 are two times smaller than typical DLA kinematics. Our results show that at z > 2, the two DLAs have a spatial extent greater than approximately 17 kpc, although the typical halo masses of disk galaxies are much larger at z ≈ 0 as compared to at z > 2. This suggests that high-z DLAs might have sizes larger than the extended H i disks seen around local galaxies. ...
Reservoirs of dense atomic gas (primarily hydrogen) contain approximately 90 per cent of the neutral gas at a redshift of 3, and contribute to between 2 and 3 per cent of the total baryons in the Universe1–4. These ‘damped Lyman α systems’—so called because they absorb Lyman α photons within and from background sources—have been studied for decades, but only through absorption lines present in the spectra of background quasars and γ-ray bursts5–10. Such pencil beams do not constrain the physical extent of the systems. Here we report integral-field spectroscopy of a bright, gravitationally lensed galaxy at a redshift of 2.7 with two foreground damped Lyman α systems. These systems are greater than 238 kiloparsecs squared in extent, with column densities of neutral hydrogen varying by more than an order of magnitude on scales of less than 3 kiloparsecs. The mean column densities are between 1020.46 and 1020.84 centimetres squared and the total masses are greater than 5.5 × 108–1.4 × 109 times the mass of the Sun, showing that they contain the necessary fuel for the next generation of star formation, consistent with relatively massive, low-luminosity primeval galaxies at redshifts greater than 2. Spectroscopy of a gravitationally lensed galaxy at a redshift of 2.7 with spatially resolved maps of two foreground damped Lyman α systems indicates a vast mass of neutral hydrogen gas, consistent with a star-forming region.
... Unfortunately, the connections between DLA/sub-DLAs and galaxies still remain far from clear, because even after decades of attempts to image the galaxies producing the absorbers (e.g., Kulkarni et al. 2001;Rao et al. 2003;Straka et al. 2010Straka et al. , 2011Péroux et al. 2011;Krogager et al. 2017), only the galaxies associated with less than a few dozen DLA/sub-DLAs have been confirmed so far. As a result, a number of different scenarios exist for the origin of DLAs, ranging from galactic disks to gas-rich dwarf galaxies to subgalactic clumps (e.g., Wolfe et al. 1986;York et al. 1986;Jimenez et al. 1999;Zwaan et al. 2008;Fynbo et al. 2013;Zafar et al. 2014;Cooke et al. 2015). ...
We report Hubble Space Telescope Cosmic Origins Spectrograph spectroscopy of 10 quasars with foreground star-forming galaxies at 0.02 < z < 0.14 within impact parameters of ∼1–7 kpc. We detect damped/sub-damped Ly α (DLA/sub-DLA) absorption in 100% of cases where no higher-redshift Lyman-limit systems extinguish the flux at the expected wavelength of Ly α absorption, obtaining the largest targeted sample of DLA/sub-DLAs in low-redshift galaxies. We present absorption measurements of neutral hydrogen and metals. Additionally, we present Green Bank Telescope 21 cm emission measurements for five of the galaxies (including two detections). Combining our sample with the literature, we construct a sample of 117 galaxies associated with DLA/sub-DLAs spanning 0 < z < 4.4, and examine trends between gas and stellar properties, and with redshift. The H i column density is anticorrelated with impact parameter and stellar mass. More massive galaxies appear to have gas-rich regions out to larger distances. The specific star formation rate (sSFR) of absorbing galaxies increases with redshift and decreases with M *, consistent with evolution of the star formation main sequence (SFMS). However, ∼20% of absorbing galaxies lie below the SFMS, indicating that some DLA/sub-DLAs trace galaxies with longer-than-typical gas-depletion timescales. Most DLA/sub-DLA galaxies with 21 cm emission have higher H i masses than typical galaxies with comparable M *. High M HI / M * ratios and high sSFRs in DLA/sub-DLA galaxies with M * < 10 ⁹ M ⊙ suggest these galaxies may be gas-rich because of recent gas accretion rather than inefficient star formation. Our study demonstrates the power of absorption and emission studies of DLA/sub-DLA galaxies for extending galactic evolution studies to previously under-explored regimes of low M * and low SFR.
... of the velocity width versus metallicity relation is in terms of the stellar mass versus metallicity relation (MZR) of galaxies, assuming galaxy luminosity scales with the dark matter halo mass. While many previous studies suggest a correlation between mass and metallicity, Zwaan et al. (2008) show that the velocity width and mass do not correlate well in local analogues of DLAs. We measured the velocity width values for the systems in our sample following the analysis of Wolfe & Prochaska (1998). ...
We present abundance measurements of the elements Zn, S, O, C, Si and Fe for four sub-DLAs at redshifts ranging from z = 2.173 to z= 2.635 using observations from the MIKE spectrograph on the Magellan telescope to constrain the chemical enrichment and star formation of gas-rich galaxies. Using weakly depleted elements O, S, and or Zn, we find the metallicities after the photoionization corrections to be [S/H] = −0.50 ± 0.11, [O/H] > −0.84, [O/H] = −1.27 ± 0.12, and [Zn/H] = +0.40 ± 0.12 for the absorbers at z = 2.173, 2.236, 2.539, and 2.635, respectively. Moreover, we are able to put constraints on the electron densities using the fine structure lines of C ii⋆ and Si ii⋆ for two of the sub-DLAs. We find that these values are much higher than the median values found in DLAs in the literature. Furthermore, we estimate the cooling rate lc = 1.20 × 10−26 erg s−1 per H atom for an absorber at z = 2.173, suggesting higher star formation rate density in this sub-DLA than the typical star formation rate density for DLAs at similar redshifts. We also study the metallicity versus velocity dispersion relation for our absorbers. Most of the absorbers follow the trend one can expect from the mass versus metallicity relation for sub-DLAs in the literature. Finally, we are able to put limits on the molecular column density from the non detections of various strong lines of CO molecules. We estimate 3σ upper limits of log N(CO,J=0) < 13.87, log N(CO,J=0) < 13.17, and log N(CO,J=0) < 13.08, respectively, from the non-detections of absorption from the J=0 level in the CO AX 0-0, 1-0, and 2-0 bands near 1544, 1510, and 1478 Å.
... Interactions are known to play an important role in moving high column density ISM to large distances outside galaxies at low-z (Hibbard 2000). Zwaan et al. (2008) argued that DLAs are likely the result of tidal interactions or outflows and unlikely to be rotation in cold disks based on their comparison of DLA velocity profiles with those of H I gas in galaxy disks. Our VATT and MMTO imaging shows a stellar extension to the south of FG at faint surface brightness levels that could be a tidal structure as well as a clump of stellar emission nearly opposite to this extension to the northeast of the galaxy. ...
We present the discovery of a low-redshift damped Ly α (DLA) system in the spectrum of background starburst galaxy SDSS J111323.88+293039.3 ( z = 0.17514). The DLA is at an impact parameter of ρ = 36 kpc from the star-forming galaxy, SDSS J111324.08+293051.2 ( z = 0.17077). We measure an H i column density of N (H i ) = 3.47 × 10 ²⁰ cm ⁻² along with multiple low-ionization species such as N i , N ii , Si ii , C ii , and Si iii . We also make an estimate of the covering fraction to be 0.883, giving us a limiting size of the DLA to be A DLA ≥ 3.3 kpc ² . Assuming a uniform column density over the entire DLA system, we estimate its mass to be M DLA ≥ 5.3 × 10 ⁶ M ⊙ . The extended illuminator and the low redshift of this DLA give us the unique opportunity to characterize its nature and the connection to its host galaxy. We measure a velocity offset of +131 km s ⁻¹ from the systemic velocity of the host for the DLA. This velocity is −84 km s ⁻¹ from the projected rotation velocity of the host galaxy as measured using a newly constructed rotation curve. Based on the size of the host galaxy, the H i column density, and the gas kinematics, we believe this DLA is tracing the warm neutral gas in the H i disk of the foreground galaxy. Our detection adds to a small set of low-redshift DLAs that have confirmed host galaxies, and is the first to be found using an extended background source.
... Interactions are known to play an important role in moving high column density ISM to large distances outside galaxies at low-z (Hibbard 2000). Zwaan et al. (2008) argued that DLAs are likely the result of tidal interactions or outflows and unlikely to be rotation in cold disks based on their comparison of DLA velocity profiles with those of H I gas in galaxy disks. Our VATT and MMTO imaging shows a stellar extension to the south of FG at faint surface brightness levels that could be a tidal structure as well as a clump of stellar emission nearly opposite to this extension to the northeast of the galaxy. ...
We present the discovery of a low-redshift damped Ly$\alpha$ (DLA) system in the spectrum of background starburst galaxy SDSS J111323.88+293039.3 ($z=0.17514$). The DLA is at an impact parameter of $\rm \rho=36~kpc$ from the star forming galaxy, SDSS J111324.08+293051.2 ($z=0.17077$). We measure an HI column density of $N($HI$)\rm =3.47\times10^{20}~cm^{-2}$ along with multiple low-ionization species such as NI, NII, SiII, CII, and SiIII. We also make an estimate of the covering fraction to be 0.883, giving us a limiting size of the DLA to be $A_{DLA}\rm \geq3.3~kpc^2$. Assuming a uniform column density over the entire DLA system, we estimate its mass to be $M_{DLA}\geq5.3\times 10^6~M_\odot$. The extended illuminator and the low redshift of this DLA give us the unique opportunity to characterize its nature and the connection to its host galaxy. We measure a velocity offset of +131 km s$^{-1}$ from the systemic velocity of the host for the DLA. This velocity is $-84$ km s$^{-1}$ from the projected rotation velocity of the host galaxy as measured using a newly constructed rotation curve. Based on the size of the host galaxy, the HI column density, and the gas kinematics, we believe this DLA is tracing the warm neutral gas in the HI disk of the foreground galaxy. Our detection adds to a small set of low-redshift DLAs that have confirmed host galaxies, and is the first to be found using an extended background source.
... The following metal transitions are used: O i 1302, C ii 1036, 1334, C iv 1548, 1550, Si ii 1190, 1193, 1260, 1304, 1526, Si iii 1206, Si iv 1393, 1402, Al ii 1670, Al iii 1854, 1862, Fe ii 1144. We exclude ±200 km/s centered on the DLA redshift (an average velocity width for typical DLA kinematic structure, Prochaska & Wolfe 1997;Zwaan et al. 2008). The number of quasars (in thousands) from the DR12Q catalogue that have a valid pixel, as set by the pipeline (non-zero inverse variance and the and_mask bit set to zero), at each wavelength. ...
The Cosmological Principle, the combined assumptions of cosmological isotropy and homogeneity, underpins the standard model of Big Bang cosmology with which we interpret astronomical observations. A new test of isotropy over the redshift range 2<z<4 and across large angular scales on the sky is presented. We use the cosmological distribution of neutral hydrogen, as probed by the Ly$\alpha$ forest seen towards distant quasars. The Sloan Digital Sky Survey provides the largest dataset of quasar spectra available to date. We use combined information from Data Releases 12 and 14 to select a sample of 142,661 quasars most suitable for this purpose. The scales covered by the data extend beyond post-inflation causality scales, thus probing initial conditions in the early universe. We identify significant spatially correlated systematic effects that can emulate cosmological anisotropy. Once these systematics have been accounted for, the data are found to be consistent with isotropy, providing an important independent check on the standard model, consistent with results from cosmic microwave background data.
... If feedback does indeed play a major role in determining the velocity widths of the DLAs, then an interesting question is whether we can find low-redshift counterparts of the DLAs and study in detail the processes giving rise to the observed ΔV 90 distribution. Using the H I emission data from the THINGS survey, Zwaan et al. (2008) derived the probability distribution function of ΔV 90 of galaxies in the local universe. This can be directly compared with the DLA ΔV 90 distribution if the lowion metals used to trace the DLAs are distributed like the neutral gas. ...
... This can be directly compared with the DLA ΔV 90 distribution if the lowion metals used to trace the DLAs are distributed like the neutral gas. Zwaan et al. (2008) argue that this is a reasonable assumption, though Prochaska et al. (2002) note that smallscale spatial variations in metallicity might affect this comparison. Like Prochaska et al. (2002), we here proceed under the assumption that these differences are not important to the kinematical properties we are studying here. ...
... Like Prochaska et al. (2002), we here proceed under the assumption that these differences are not important to the kinematical properties we are studying here. Zwaan et al. (2008) find that the distribution of ΔV 90 for the THINGS galaxies is sharply peaked around ∼30 km s −1 , a factor two lower than the observed peak in the distribution for higher-redshift DLAs as found by Prochaska et al. (2008). They use the Yun et al. (1993a) H I data, along with VLA archival data, to determine the distribution of ΔV 90 in M82 and find values similar to those found in DLAs. ...
We present a 3° × 3°, 105-pointing, high-resolution neutral hydrogen (H i) mosaic of the M81 galaxy triplet, (including the main galaxies M81, M82, and NGC 3077, as well as dwarf galaxy NGC 2976) obtained with the Very Large Array C and D arrays. This H i synthesis mosaic uniformly covers the entire area and velocity range of the triplet. The observations have a resolution of ~20'' or ~420 pc. The data reveal many small-scale anomalous velocity features highlighting the complexity of the interacting M81 triplet. We compare our data with Green Bank Telescope observations of the same area. This comparison provides evidence for the presence of a substantial reservoir of low-column density gas in the northern part of the triplet, probably associated with M82. Such a reservoir is not found in the southern part. We report a number of newly discovered kpc-sized low-mass H i clouds with H i masses of a few times 10⁶M ⊙. A detailed analysis of their velocity widths show that their dynamical masses are much larger than their baryonic masses, which could indicate the presence of dark matter if the clouds are rotationally supported. However, due to their spatial and kinematical association with H i tidal features, it is more likely that the velocity widths indicate tidal effects or streaming motions. We do not find any clouds that are not associated with tidal features down to an H i mass limit of a few times 10⁴M ⊙. We compare the H i column densities with resolved stellar density maps and find a star formation threshold around 3–6 × 10²⁰ cm⁻². We investigate the widths of the H i velocity profiles in the triplet and find that extreme velocity dispersions can be explained by a superposition of multiple components along the line of sight near M81 as well as winds or outflows around M82. The velocity dispersions found are high enough that these processes could explain the linewidths of damped-Lyα absorbers observed at high redshift.
... There are also contributions to the velocity spread from merging galaxies, outflows from galactic winds, galactic infall, etc, which can increase ∆V 90 for low-mass galaxies above the values expected due to rotation. For galaxies in the local Universe, where the mass can be estimated directly, Zwaan et al. (2008) find only a weak relation between ∆V 90 and mass. Finally, the relation between [Z/H] and ∆V 90 itself has a large spread, ≈ 1.5 dex in metallicity at a given ∆V 90 (see Fig.6[A] of . ...
We report results from a programme aimed at investigating the temperature of
neutral gas in high-redshift damped Lyman-$\alpha$ absorbers (DLAs). This
involved (1) HI 21cm absorption studies of a large DLA sample, (2) VLBI studies
to measure the low-frequency quasar core fractions, and (3) optical/ultraviolet
spectroscopy to determine DLA metallicities and velocity widths.
Including literature data, our sample consists of 37 DLAs with estimates of
the spin temperature $T_s$ and the covering factor. We find a strong $4\sigma$)
difference between the $T_s$ distributions in high-z (z>2.4) and low-z (z<2.4)
DLA samples. The high-z sample contains more systems with high $T_s$ values,
$\gtrsim 1000$ K. The $T_s$ distributions in DLAs and the Galaxy are also
clearly (~$6\sigma$) different, with more high-$T_s$ sightlines in DLAs than in
the Milky Way. The high $T_s$ values in the high-z DLAs of our sample arise due
to low fractions of the cold neutral medium.
For 29 DLAs with metallicity [Z/H] estimates, we confirm the presence of an
anti-correlation between $T_s$ and [Z/H], at $3.5\sigma$ significance via a
non-parametric Kendall-tau test. This result was obtained with the assumption
that the DLA covering factor is equal to the core fraction. Monte Carlo
simulations show that the significance of the result is only marginally
decreased if the covering factor and the core fraction are uncorrelated, or if
there is a random error in the inferred covering factor.
We also find evidence for redshift evolution in DLA $T_s$ values even for the
z>1 sub-sample. Since z>1 DLAs have angular diameter distances comparable to or
larger than those of the background quasars, they have similar efficiency in
covering the quasars. Low covering factors in high-z DLAs thus cannot account
for the observed redshift evolution in spin temperatures. (Abstract abridged.)
... Bouché et al. (2006), however, find an anti-correlation between the Mg II equivalent width and the estimated halo mass based upon an indirect mass indicator. Also, Zwaan et al. (2008) show that the velocity width and mass do not correlate well in local analogues of DLAs. ...
We present chemical abundance measurements from high-resolution
observations of five sub-damped Lyman α absorbers (sub-DLAs) at
1.7 < z < 2.4 observed with the Magellan Inamori Kyocera Echelle
(MIKE) spectrograph on the 6.5-m Magellan II (Clay) telescope. Lines of
Zn II, Mg I, Mg II, Al II, Al III, S II, Si II, Si IV, C II, C II*, C
IV, Ni II, Mn II and Fe II were detected and column densities were
determined. The metallicity of the absorbing gas, inferred from the
nearly undepleted element Zn, is in the range of <-0.95 to +0.25 dex
for the five absorbers in our sample, with three of the systems being
near-solar or supersolar. We also investigate the effect of ionization
on the observed abundances using photoionization modelling. Combining
our data with other sub-DLA and DLA data from the literature, we report
the most complete existing determination of the metallicity versus
redshift relation for sub-DLAs and DLAs. We confirm the suggestion from
previous investigations that sub-DLAs are, on average, more metal rich
than DLAs and may evolve faster. We also discuss relative abundances and
abundance ratios in these absorbers. The more metal-rich systems show
significant dust depletion levels, as suggested by the ratios [Zn/Cr]
and [Zn/Fe]. For the majority of the systems in our sample, the [Mn/Fe]
versus [Zn/H] trend is consistent with that seen previously for lower
redshift sub-DLAs. We also measure the velocity width values for the
sub-DLAs in our sample from unsaturated absorption lines of Fe II
λλ2344, 2374, 2600 Å, and examine where these
systems lie in a plot of metallicity versus velocity dispersion.
Finally, we examine cooling rate versus H I column density in these
sub-DLAs, and compare this with the data from DLAs and the Milky Way
interstellar medium. We find that most of the systems in our sample show
higher cooling rate values compared to those seen in the DLAs.
... Different models attribute the absorption to either galactic winds [e.g., Bouché (2008); Oppenheimer & Davé (2008)] , or to cool clumps condensing out from the virialized gaseous halos of galaxies [e.g., Mo & Miralda-Escude (1996); Maller & Bullock (2004); Kaufmann et al. (2008) ] related , perhaps, to infalling material ( Kereš & Hernquist 2009). Alternative explanations relate some systems to gravitationally bound minihalos (Kepner et al. 1999; Sternberg et al. 2002; Gnat & Sternberg 2004) or to galaxy disks (Wagoner 1967; Prochaska & Wolfe 1997; Charlton & Churchill 1996; Prochaska & Wolfe 1998; Zwaan et al. 2005 Zwaan et al. , 2008). While some models are qualitatively consistent with some observational constraints [e.g., Srianand & Khare (1994); Chelouche et al. (2008);, many of the recently discovered statistical properties of Mg II systems have not been addressed by theoretical works, and the following questions remain: What is the origin of strong metal systems? ...
We argue that most strong intervening metal absorption line systems, where the rest equivalent width of the MgII 2796A line is >0.5A, are interstellar material in, and outflowing from, star-forming disks. We show that a version of the Kennicutt-Schmidt law is readily obtained if the MgII equivalent widths are interpreted as kinematic broadening from absorbing gas in outflowing winds originating from star-forming galaxies. Taking a phenomenological approach and using a set of observational constraints available for star-forming galaxies, we are able to account for the density distribution of strong MgII absorbers over cosmic time. The association of intervening material with star-forming disks naturally explains the metallicity and dust content of strong MgII systems as well as their high HI column densities, and does not require the advection of metals from compact star-forming regions into the galaxy halos to account for the observations. We find that galaxies with a broad range of luminosities can give rise to absorption of a given rest-equivalent width, and discuss possible observational strategies to better quantify true galaxy-absorber associations and further test our model. We show that the redshift evolution in the density of absorbers closely tracks the star formation history of the universe and that strong intervening systems can be used to directly probe the physics of both bright and faint galaxies over a broad redshift range. By identifying strong intervening systems with galaxy disks and quantifying a version of the Kennicutt-Schmidt law that applies to them, a new probe of the interstellar medium is found which provides complementary information to that obtained through emission studies of galaxies. Implications of our results for galaxy feedback and enrichment of the intergalactic medium are discussed. [abridged] Comment: 23 pages, 15 figures
