scholarly journals A Direct Detection of Gas Accretion: The Lyman Limit System in 3C 232

2010 ◽  
Vol 27 (3) ◽  
pp. 256-264 ◽  
Author(s):  
John T. Stocke ◽  
Brian A. Keeney ◽  
Charles W. Danforth
Keyword(s):  
Hubble Space Telescope ◽  
Direct Detection ◽  
Uv Spectroscopy ◽  
Cosmic Time ◽  
Physical Conditions ◽  
New Instrument ◽  
Luminous Galaxies ◽  
Gas Accretion ◽  
Velocity Cloud ◽  
Quasar Spectrum

AbstractThe gas added to and removed from galaxies over cosmic time greatly affects their stellar populations and star formation rates. QSO absorption line studies in close QSO/galaxy pairs create a unique opportunity to study the physical conditions and kinematics of this gas. Here we present new Hubble Space Telescope (HST) images of the QSO/galaxy pair, 3C 232/NGC 3067. The quasar spectrum contains a Lyman limit (NHi = 1 × 1020 cm−2) absorption system (LLS) at cz = 1421 km s−1 that is associated with the nearby Sab galaxy NGC 3067. Previous work identifies this absorber as a high-velocity cloud (HVC) in NGC 3067 but the kinematics of the absorbing gas, infalling or outflowing, were uncertain. The HST images presented here establish the orientation of NGC 3067 and so establish that the LLS/HVC is infalling. Using this system as a prototype, we extend these results to higher-z MgII/LLS to suggest that Mgii/LLSs are a sightline sampling of the so-called ‘cold mode accretion’ (CMA) infalling onto luminous galaxies. To match the observed MgII absorber statistics, the CMA must be more highly ionised at higher redshifts. The key observations needed to further the study of low-z LLSs is HST UV spectroscopy, for which a new instrument, the Cosmic Origins Spectrograph, has just been installed greatly enhancing our observational capabilities.

scholarly journals The Low-redshift Intergalactic Medium

1999 ◽  
Vol 16 (1) ◽  
pp. 95-99 ◽  
Author(s):  
J. Michael Shull ◽  
Steven V. Penton ◽  
John T. Stocke
Keyword(s):  
Galaxy Formation ◽  
Large Scale ◽  
Intergalactic Medium ◽  
Hubble Space Telescope ◽  
Characteristic Size ◽  
Baryon Density ◽  
Frequency Space ◽  
Physical Conditions ◽  
Low Metallicity ◽  
Set Up

AbstractThe low-redshift Lyα forest of absorption lines provides a probe of large-scale baryonic structures in the intergalactic medium, some of which may be remnants of physical conditions set up during the epoch of galaxy formation. We discuss our recent Hubble Space Telescope (HST) observations and interpretation of low-z Lyα clouds toward nearby Seyferts and QSOs, including their frequency, space density, estimated mass, association with galaxies, and contribution to Ωb. Our HST/GHRS detections of ∼ 70 Lyα absorbers with Nhi ≥ 1012·6 cm−2 along 11 sightlines covering pathlength Δ(cz) = 114,000 km s−1 show f (>Nhi) α Nhi−0·63±0·04 and a line frequency dN/dz = 200 ± 40 for Nhi > 1012·6 cm−2 (one every 1500 km s−1 of redshift). A group of strong absorbers toward PKS 2155–304 may be associated with gas (400–800) kpc from four large galaxies, with low metallicity (≤0·003 solar) and D/H ≤ 2 × 10−4. At low-z, we derive a metagalactic ionising radiation field from AGN of J0 = × 10−23 erg cm−2 s−1 Hz−1 sr−1 and a Lyα-forest baryon density Ωb =(0·008 ± 0·004)[J−23N14b100]½ for clouds of characteristic size b = (100 kpc)b100.

scholarly journals The age–chemical abundance structure of the Galactic disc – II. α-dichotomy and thick disc formation

2020 ◽  
Vol 497 (2) ◽  
pp. 2371-2384 ◽  
Author(s):  
Jianhui Lian ◽  
Daniel Thomas ◽  
Claudia Maraston ◽  
Timothy C Beers ◽  
Christian Moni Bidin ◽  
...  
Keyword(s):  
Star Formation ◽  
Cosmic Time ◽  
Theoretical Models ◽  
Bimodal Distribution ◽  
Chemical Abundance ◽  
Secular Evolution ◽  
Thick Disc ◽  
Star Formation Activity ◽  
Gas Accretion ◽  
Disc Formation

ABSTRACT We extend our previous work on the age–chemical abundance structure of the Galactic outer disc to the inner disc (4 < r < 8  kpc) based on the SDSS/APOGEE survey. Different from the outer disc, the inner disc stars exhibit a clear bimodal distribution in the [Mg/Fe]–[Fe/H] plane. While a number of scenarios have been proposed in the literature, it remains challenging to recover this bimodal distribution with theoretical models. To this end, we present a chemical evolution model embedding a complex multiphase inner disc formation scenario that matches the observed bimodal [Mg/Fe]–[Fe/H] distribution. In this scenario, the formation of the inner disc is dominated by two main starburst episodes $6\,$Gyr apart with secular, low-level star formation activity in between. In our model, the first starburst occurs at early cosmic times ($t\sim 1\,$ Gyr) and the second one $6\,$ Gyr later at a cosmic time of $t\sim 7\,$ Gyr. Both these starburst episodes are associated with gas accretion events in our model, and are quenched rapidly. The first starburst leads to the formation of the high-α sequence, and the second starburst leads to the formation of the metal-poor low-α sequence. The metal-rich low-α stars, instead, form during the secular evolution phase between the two bursts. Our model shows that the α-dichotomy originates from the rapid suppression of star formation after the first starburst. The two starburst episodes are likely to be responsible for the formation of the geometric thick disc (z >1 kpc), with the old inner thick disc and the young outer thick disc forming during the first and the second starbursts, respectively.

scholarly journals Element Abundances in Magellanic Cloud H II Regions from Carbon to Argon

1999 ◽  
Vol 190 ◽  
pp. 266-272 ◽  
Author(s):  
Donald R. Garnett
Keyword(s):  
Heavy Element ◽  
Hubble Space Telescope ◽  
Uv Spectroscopy ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
H Ii Regions ◽  
Ionized Gas ◽  
Mixing Processes ◽  
Element Abundances ◽  
C And N

I review measurements of heavy element abundances within H II regions in the Magellanic Clouds, highlighting in particular improved determinations of carbon abundances based on UV spectroscopy with Hubble Space Telescope. In general, the Magellanic Cloud H II regions show average underabundances in O, Ne, and S (relative to their Galactic counterparts) that are similar to those measured in Magellanic Cloud stars. However, comparison of stars and ionized gas shows discrepancies in C and N abundances that may be related to recently recognized mixing processes that may be operating in massive stars.

scholarly journals Hubble Space Telescope Far-UV Spectroscopy of the Short Orbital Period Recurrent Nova CI Aql: Implications for White Dwarf Mass Evolution

2019 ◽  
Vol 872 (1) ◽  
pp. 68
Author(s):  
Edward M. Sion ◽  
R. E. Wilson ◽  
Patrick Godon ◽  
Sumner Starrfield ◽  
Robert E. Williams ◽  
...  
Keyword(s):  
Orbital Period ◽  
White Dwarf ◽  
Hubble Space Telescope ◽  
Uv Spectroscopy ◽  
Space Telescope ◽  
Recurrent Nova

scholarly journals THE DIRECT DETECTION OF COOL, METAL-ENRICHED GAS ACCRETION ONTO GALAXIES AT z ∼ 0.5

2012 ◽  
Vol 747 (2) ◽  
pp. L26 ◽  
Author(s):  
Kate H. R. Rubin ◽  
J. Xavier Prochaska ◽  
David C. Koo ◽  
Andrew C. Phillips
Keyword(s):  
Direct Detection ◽  
Gas Accretion

S[CLC]i/O Abundance Ratios in Extragalactic H[/CLC] [CSC]ii[/CSC] Regions from [ITAL]Hubble Space Telescope[/ITAL] UV Spectroscopy

1995 ◽  
Vol 449 (1) ◽  
Author(s):  
D. R. Garnett, ◽  
R. J. Dufour, ◽  
M. Peimbert, ◽  
S. Torres-Peimbert, ◽  
G. A. Shields, ◽  
...  
Keyword(s):  
Hubble Space Telescope ◽  
Uv Spectroscopy ◽  
Space Telescope

scholarly journals From galactic nuclei to the halo outskirts: tracing supermassive black holes across cosmic history and environments

2020 ◽  
Vol 495 (4) ◽  
pp. 4681-4706 ◽  
Author(s):  
David Izquierdo-Villalba ◽  
Silvia Bonoli ◽  
Massimo Dotti ◽  
Alberto Sesana ◽  
Yetli Rosas-Guevara ◽  
...  
Keyword(s):  
Black Holes ◽  
Cosmic Time ◽  
Mass Function ◽  
Supermassive Black Holes ◽  
Dominant Type ◽  
Central Regions ◽  
Mass Assembly ◽  
The One ◽  
Gas Accretion ◽  
The Impact

ABSTRACT We study the mass assembly and spin evolution of supermassive black holes (BHs) across cosmic time as well as the impact of gravitational recoil on the population of nuclear and wandering BHs (wBHs) by using the semi-analytical model L-Galaxies run on top of Millennium merger trees. We track spin changes that BHs experience during both coalescence events and gas accretion phases. For the latter, we assume that spin changes are coupled with the bulge assembly. This assumption leads to predictions for the median spin values of z = 0 BHs that depend on whether they are hosted by pseudo-bulges, classical bulges or ellipticals, being $\overline{a} \sim 0.9$, 0.7 and 0.4, respectively. The outcomes of the model display a good consistency with $z \le 4$ quasar luminosity functions and the $z = 0$ BH mass function, spin values, and BH correlation. Regarding the wBHs, we assume that they can originate from both the disruption of satellite galaxies (orphan wBH) and ejections due to gravitational recoils (ejected wBH). The model points to a number density of wBHs that increases with decreasing redshift, although this population is always $\rm {\sim}2\, dex$ smaller than the one of nuclear BHs. At all redshifts, wBHs are typically hosted in $\rm {\it M}_{halo} \gtrsim 10^{13} \, M_{\odot }$ and $\rm {\it M}_{stellar} \gtrsim 10^{10} \, M_{\odot }$, being orphan wBHs the dominant type. Besides, independently of redshift and halo mass, ejected wBHs inhabit the central regions (${\lesssim}\rm 0.3{\it R}_{200}$) of the host DM halo, while orphan wBH linger at larger scales (${\gtrsim}\rm 0.5{\it R}_{200}$). Finally, we find that gravitational recoils cause a progressive depletion of nuclear BHs with decreasing redshift and stellar mass. Moreover, ejection events lead to changes in the predicted local BH–bulge relation, in particular for BHs in pseudo-bulges, for which the relation is flattened at $\rm {\it M}_{bulge} \gt 10^{10.2}\, M_{\odot }$ and the scatter increase up to ${\sim}\rm 3\, dex$.

scholarly journals Mentari: A pipeline to model the galaxy SED using semi analytic models

2019 ◽  
Vol 15 (S341) ◽  
pp. 119-123
Author(s):  
Dian Triani ◽  
Darren Croton ◽  
Manodeep Sinha
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Spectral Energy Distribution ◽  
Cosmic Time ◽  
Spectral Energy ◽  
Chemical Enrichment ◽  
The Galaxy ◽  
History Of ◽  
Gas Accretion ◽  
Analytic Models

AbstractWe build a theoretical picture of how the light from galaxies evolves across cosmic time. In particular, we predict the evolution of the galaxy spectral energy distribution (SED) by carefully integrating the star formation and metal enrichment histories of semi-analytic model (SAM) galaxies and combining these with stellar population synthesis models which we call mentari. Our SAM combines prescriptions to model the interplay between gas accretion, star formation, feedback process, and chemical enrichment in galaxy evolution. From this, the SED of any simulated galaxy at any point in its history can be constructed and compared with telescope data to reverse engineer the various physical processes that may have led to a particular set of observations. The synthetic SEDs of millions of simulated galaxies from mentari can cover wavelengths from the far UV to infrared, and thus can tell a near complete story of the history of galaxy evolution.

scholarly journals Physical conditions and chemistry of molecular gas in galactic centers

2013 ◽  
Vol 9 (S303) ◽  
pp. 15-28
Author(s):  
Susanne Aalto
Keyword(s):  
Milky Way ◽  
Stimulated Emission ◽  
Molecular Gas ◽  
Nuclear Activity ◽  
X Ray ◽  
Physical Conditions ◽  
Luminous Galaxies ◽  
Mass Outflow ◽  
Driving Source ◽  
Luminous Infrared Galaxy

AbstractStudying the molecular phase of the interstellar medium in galaxy nuclei is fundamental for the understanding of the onset and evolution of star formation and the growth of supermassive black holes. We can use molecules as observational tools exploiting them as tracers of chemical, physical and dynamical conditions. The molecular physical conditions in galaxy centers show large variety among galaxies, but in general the average gas densities (traced by e.g. HCN) and temperatures (probed by e.g. H2CO, NH3) are greater than in their disks. Molecular gas and dust is being funneled to the centers of galaxies by spiral arms, bars, and interactions - and one example of this is the minor merger NGC1614. Gas surface densities are also greater in galaxy nuclei and in extreme cases they become orders of magnitudes larger than what we find in the center of our own Milky Way. We can use IR excited molecular emission to probe the very inner regions of galaxies with deeply obscured nuclei where N(H2)>1024 cm−2 - for example the luminous infrared galaxy (LIRG) NGC4418. Abundances of key molecules such as HCN, HCO+, HNC, HC3N, CN, H3O+ are important tools in identifying the nature of buried activity and its evolution. Standard astrochemical scenarios (including X-ray Dominated regions (XDRs) and Photon Dominated Regions (PDRs)) are briefly discussed in this review and how we can use molecules to distinguish between them. High resolution studies are often necessary to separate effects of excitation and radiative transfer from those of chemistry - one example is absorption and effects of stimulated emission in the ULIRG Arp220. The nuclear activity in luminous galaxies often drives outflows and winds and in some cases molecular gas is being entrained in the outflows. Sometimes the molecular gas is carrying the bulk of the momentum. We can study the structure and physical conditions of the molecular gas to constrain the mass outflow rates and the evolution and nature of the driving source and two examples are discussed here: NGC1377 and Mrk231.

scholarly journals WatSen: searching for clues for water (and life) on Mars

2006 ◽  
Vol 5 (3) ◽  
pp. 211-219 ◽  
Author(s):  
Monica M. Grady
Keyword(s):  
Large Scale ◽  
Direct Detection ◽  
Spectral Characteristics ◽  
Mineral Chemistry ◽  
Small Scale ◽  
Martian Surface ◽  
Ir Detector ◽  
Local Evidence ◽  
New Instrument ◽  
Life On Mars

There is plenty of evidence for fluid on Mars: large-scale (planet-wide) features have been captured over four decades by a procession of orbiting satellites equipped with cameras with increasingly higher spatial resolutions. Imagery of the surface shows channels, valleys, ice-caps, etc. Small-scale, more local evidence for fluid has come from images obtained by rovers on the Martian surface. Images that water produced many of the features are supported by spectroscopic measurements (again both planet-wide and local) over a range of wavelengths, which show the presence of minerals generally only produced in the presence of water (haemetite, jarosite, etc.). Results from meteorites continue this picture of fluid activity taking place over significant periods of Mars' history. Despite all these indicators of water, direct detection of water has never been performed. We have reviewed the evidence for water on Mars' surface, and have described WatSen, a combined humidity sensor and infrared IR detector, which can be employed to search for water at and below Mars' surface. WatSen is designed to be part of the suite of instruments on the mole that will be deployed as part of the Geophysics and Environment Package on ExoMars. The objectives of the package are as follows: (i) to detect water within Martian soil by measuring humidity and IR spectral characteristics of the substrate at surface and at depth; (ii) to determine the mineralogy and mineral chemistry of surface soils (this measurement will provide the mineralogical context for the elemental results that come from other instruments mounted on the landing platform); (iii) to determine how mineralogy changes with depth. The utility of WatSen is that it will not only detect the presence of water, but will also be able to record which minerals are present and their chemistry; it is also sensitive to many organic species. WatSen is a new instrument concept specifically designed to search for clues of the presence of water, and to look for evidence of life on Mars.

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