scholarly journals Local HI: Constraints on the Evolution of the HI Content of the Universe

1997 ◽  
Vol 14 (1) ◽  
pp. 31-36 ◽  
Author(s):  
F. H. Briggs
Keyword(s):  
Star Formation ◽  
Absorption Line ◽  
Galaxy Evolution ◽  
Column Density ◽  
Absorption Lines ◽  
Reliable Measure ◽  
Redshift Range ◽  
Neutral Gas ◽  
Present Rate ◽  
The Universe

AbstractAnalyses of QSO absorption lines show that the HI content has evolved over the redshift range z = 5 to z = 0. The 21-cm line measurements of the z = 0 HI content avoid several biases inherent in the absorption-line technique, such as the influence of evolving dust content in the absorbers, and will produce a reliable measure to anchor theories of galaxy evolution. Examples of important questions to be addressed by local HI surveys are: (1) Is there a significant population of gas-rich galaxies or intergalactic clouds that is missing from the census of optically selected galaxies? (2) Is there an adequate reservoir of neutral gas to substantially prolong star formation at its present rate? (3) Are there massive objects of such low HI column density that they can have escaped detection in the ‘unbiased’ HI surveys that have been conducted so far?

scholarly journals H i imaging of dwarf star-forming galaxies: masses, morphologies, and gas deficiencies

2020 ◽  
Vol 498 (4) ◽  
pp. 4745-4789
Author(s):  
S Jaiswal ◽  
A Omar
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Surface Density ◽  
Column Density ◽  
Line Emission ◽  
Scaling Relations ◽  
Dwarf Star ◽  
Star Forming ◽  
Average Value ◽  
Tidal Interactions

ABSTRACT The Giant Meter-wave Radio Telescope observations of the H i 21 cm-line emission from 13 nearby dwarf star-forming galaxies are presented. These galaxies are selected from the catalogues of Wolf−Rayet galaxies having very young (≤10 Myr) star formation. The ranges of star formation rates and stellar masses of the sample galaxies are 0.03–1.7 M⊙ yr−1 and 0.04–22.3 × 108 M⊙, respectively. The H i line emission is detected from 12 galaxies with peak column density >1 × 1021 cm−2. The 3σ H i column density sensitivities per channel width of 7 km s−1 for low (60 arcsec × 60 arcsec) resolution images are in the range 0.8–1.9 × 1019 cm−2. The H i channel images, moment images, global profiles, and mass surface density profiles are presented here. The average value of the peak H i mass surface density is estimated to be ∼2.5 M⊙ pc−2, which is significantly less compared to that in massive spiral galaxies. The scaling relations of $(M_{stars} + M_{\rm H\, I} + M_{\rm He})$versus Mdyn, gas fraction versus MB, $M_{\rm H\, I}$versus Mstars, H i-to-stellar mass ratio versus Mstars, and $M_{\rm H\, I}$versus $D_{\rm H\, I}$for the sample galaxies are estimated. These scaling relations can be used to constraint the key parameters in the galaxy evolution models. These galaxies are residing in group environment with galaxy density up to eight galaxy Mpc−3. An H i mass deficiency (with DEFH i > 0.3) is noticed in majority of galaxies for their optical diameters as compared to galaxies in field environments. Clear signatures of tidal interactions in these galaxies could be inferred using the H i images. Isolated H i clouds without known optical counterparts are seen in the vicinity of several galaxies. H i emission envelope is found to be having an offset from the optical envelope in several galaxies. Consistent with the previous studies on galaxy evolution in group environments, tidal interactions seem to play an important role in triggering recent star formation.

scholarly journals Widespread star formation inside galactic outflows

2019 ◽  
Vol 485 (3) ◽  
pp. 3409-3429 ◽  
Author(s):  
R Gallagher ◽  
R Maiolino ◽  
F Belfiore ◽  
N Drory ◽  
R Riffel ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Scaling Relations ◽  
Molecular Gas ◽  
Distant Galaxies ◽  
Major Mode ◽  
Galactic Outflows ◽  
The Universe ◽  
Integral Field

Abstract Several models have predicted that stars could form inside galactic outflows and that this would be a new major mode of galaxy evolution. Observations of galactic outflows have revealed that they host large amounts of dense and clumpy molecular gas, which provide conditions suitable for star formation. We have investigated the properties of the outflows in a large sample of galaxies by exploiting the integral field spectroscopic data of the large MaNGA-SDSS4 galaxy survey. We find evidence for prominent star formation occurring inside at least 30 per cent of the galactic outflows in our sample, whilst signs of star formation are seen in up to half of the outflows. We also show that even if star formation is prominent inside many other galactic outflows, this may have not been revealed as the diagnostics are easily dominated by the presence of even faint active galactic nucleus and shocks. If very massive outflows typical of distant galaxies and quasars follow the same scaling relations observed locally, then the star formation inside high-z outflows can be up to several 100 $\rm M_{\odot }~yr^{-1}$ and could contribute substantially to the early formation of the spheroidal component of galaxies. Star formation in outflows can also potentially contribute to establishing the scaling relations between black holes and their host spheroids. Moreover, supernovae exploding on large orbits can chemically enrich in situ and heat the circumgalactic and intergalactic medium. Finally, young stars ejected on large orbits may also contribute to the reionization of the Universe.

Xvoigt: An Interactive Absorption Line Fitting Program for the X Window System

1995 ◽  
Vol 12 (2) ◽  
pp. 239-243 ◽  
Author(s):  
David P. Max ◽  
Geoff Bailey
Keyword(s):  
Absorption Line ◽  
Column Density ◽  
Velocity Dispersion ◽  
Absorption Lines ◽  
Signal To Noise ◽  
Window System ◽  
Profile Fitting ◽  
X Window ◽  
Line Fitting ◽  
Line Analysis

AbstractWe have developed an easy-to-use, mouse-driven program for the interactive fitting of interstellar absorption lines in high-resolution astronomical spectra. The program, Xvoigt, gives values for the column density and velocity dispersion of the absorbing clouds. It runs under the popular X Window system available on most workstations, and offers significant enhancements over existing profile-fitting software. Xvoigt can be an important adjunct to automatic programs for fitting absorption lines in low to moderate signal-to-noise QSO or other spectra, and is ideal for demonstrating the details and difficulties of absorption line analysis.

scholarly journals The Cosmic Baryon and Metal Cycles

2020 ◽  
Vol 58 (1) ◽  
pp. 363-406 ◽  
Author(s):  
Céline Péroux ◽  
J. Christopher Howk
Keyword(s):  
Star Formation ◽  
Mass Density ◽  
Formation Rate ◽  
Cosmic Time ◽  
Dust Content ◽  
Star Formation History ◽  
Molecular Gas ◽  
Neutral Gas ◽  
Formation History ◽  
The Universe

Characterizing the relationship between stars, gas, and metals in galaxies is a critical component of understanding the cosmic baryon cycle. We compile contemporary censuses of the baryons in collapsed structures and their chemical makeup and dust content. We show the following: ▪  The [Formula: see text] mass density of the Universe is well determined to redshifts [Formula: see text] and shows minor evolution with time. New observations of molecular hydrogen reveal its evolution mirrors that of the global star-formation rate density, implying a universal cosmic molecular gas depletion timescale. The low-redshift decline of the star-formation history is thus driven by the lack of molecular gas supply due to a drop in net accretion rate related to the decreased growth of dark matter halos. ▪  The metal mass density in cold gas ([Formula: see text] K) contains virtually all the metals produced by stars for [Formula: see text]. At lower redshifts, the contributors to the total amount of metals are more diverse; at [Formula: see text], most of the observed metals are bound in stars. Overall, there is little evidence for a “missing metals problem” in modern censuses. ▪  We characterize the dust content of neutral gas over cosmic time, finding the dust-to-gas and dust-to-metals ratios fall with decreasing metallicity. We calculate the cosmological dust mass density in the neutral gas up to [Formula: see text]. There is good agreement between multiple tracers of the dust content of the Universe.

GALAXY EVOLUTION THROUGH THE COSMIC TIME

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1371-1377
Author(s):  
T. P. IDIART ◽  
J. A. F. PACHECO ◽  
J. SILK
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Cosmic Time ◽  
Evolutionary Model ◽  
Stellar Populations ◽  
Elliptical Galaxies ◽  
Star Formation Activity ◽  
Formation And Evolution ◽  
The Universe

Elliptical galaxies are the best systems to study the early star formation activity in the universe. This work aims to understand the formation and evolution of these objects through the study of the integrated properties of their stellar populations. Here an evolutionary model is developed and their predicted spectrophotometric properties are presented.

scholarly journals Multiscale cosmic web detachments, connectivity, and preprocessing in the supercluster SCl A2142 cocoon

2020 ◽  
Vol 641 ◽  
pp. A172
Author(s):  
Maret Einasto ◽  
Boris Deshev ◽  
Peeter Tenjes ◽  
Pekka Heinämäki ◽  
Elmo Tempel ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Stellar Populations ◽  
Main Body ◽  
Low Density ◽  
Very Old ◽  
Global Environmental ◽  
Wide Range ◽  
Local Densities ◽  
The Universe

Context. Superclusters of galaxies and their surrounding low-density regions (cocoons) represent dynamically evolving environments in which galaxies and their systems form and evolve. While evolutionary processes of galaxies in dense environments are extensively studied at present, galaxy evolution in low-density regions has received less attention. Aims. We study the properties, connectivity, and galaxy content of groups and filaments in the A2142 supercluster (SCl A2142) cocoon to understand the evolution of the supercluster with its surrounding structures and the galaxies within them. Methods. We calculated the luminosity-density field of SDSS galaxies and traced the SCl A2142 cocoon boundaries by the lowest luminosity-density regions that separate SCl A2142 from other superclusters. We determined galaxy filaments and groups in the cocoon and analysed the connectivity of groups, the high density core (HDC) of the supercluster, and the whole of the supercluster. We compared the distribution and properties of galaxies with different star-formation properties in the supercluster and in the cocoon. Results. The supercluster A2142 and the long filament that is connected to it forms the longest straight structure in the Universe detected so far, with a length of approximately 75 h−1 Mpc. The connectivity of the cluster A2142 and the whole supercluster is C = 6 − 7; poor groups exhibit C = 1 − 2. Long filaments around the supercluster’s main body are detached from it at the turnaround region. Among various local and global environmental trends with regard to the properties of galaxies and groups, we find that galaxies with very old stellar populations lie in systems across a wide range of richness from the richest cluster to poorest groups and single galaxies. They lie even at local densities as low as D1 <  1 in the cocoon and up to D1 >  800 in the supercluster. Recently quenched galaxies lie in the cocoon mainly in one region and their properties are different in the cocoon and in the supercluster. The star-formation properties of single galaxies are similar across all environments. Conclusions. The collapsing main body of SCl A2142 with the detached long filaments near it are evidence of an important epoch in the supercluster evolution. There is a need for further studies to explore possible reasons behind the similarities between galaxies with very old stellar populations in extremely different environments, as well as mechanisms for galaxy quenching at very low densities. The presence of long, straight structures in the cosmic web may serve as a test for cosmological models.

scholarly journals Blue Compact Dwarf Galaxies: Laboratories for probing the Primordial Universe

2008 ◽  
Vol 4 (S255) ◽  
pp. 348-360 ◽  
Author(s):  
Trinh X. Thuan
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Dwarf Galaxies ◽  
Big Bang ◽  
The Sun ◽  
Big Bang Nucleosynthesis ◽  
Star Forming ◽  
The Universe

AbstractBlue Compact Dwarf (BCD) galaxies are the most metal-deficient star-forming galaxies known in the universe, with metallicities ranging from 1/40 to 1/3 that of the Sun. I review how they constitute excellent nearby laboratories for studying big bang nucleosynthesis and star formation and galaxy evolution processes in a nearly primordial environment.

scholarly journals The Evolution of Neutral Gas in the Universe

2006 ◽  
Vol 2 (S235) ◽  
pp. 440-440
Author(s):  
David Turnshek ◽  
Sandhya Rao ◽  
Eric Monier ◽  
Daniel Nestor ◽  
Anna Quider
Keyword(s):  
Absorption Line ◽  
Hubble Space Telescope ◽  
Reference List ◽  
Space Telescope ◽  
Neutral Gas ◽  
The Universe ◽  
Initial Results ◽  
Gas Component

AbstractWe give references to some of our work on the properties and evolution of the neutral gas component of the Universe (see reference list). The bulk of the observed neutral gas has been detected by identifying intervening damped Lyα (DLA) quasar absorption-line systems with N(H) ≥2 × 1020 atoms cm−2. We also present some initial results from a program to identify DLA absorbers near redshift z = 0.5 using Hubble Space Telescope ACS prism spectra (see Figure 1).

scholarly journals Galaxy Evolution from QSO Absorption-Line Selected Samples

1996 ◽  
Vol 171 ◽  
pp. 295-298 ◽  
Author(s):  
Mark Dickinson ◽  
Charles C. Steidel
Keyword(s):  
Absorption Line ◽  
Galaxy Evolution ◽  
Absorption Lines

Although a connection between certain classes of QSO absorption line systems and gas associated with galaxies was hypothesized long ago, the first systematic evidence supporting this was provided by Bergeron & Boissé (1991). Observing QSOs with known Mgll absorption lines at zabs < zQSO, they identified galaxies near the QSO sightline and spectroscopically confirmed that their redshifts matched those of the MgII absorption doublet.

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