* Astronomy

Members Login

Post Info

TOPIC: z=2-7 Star-Formation Plateau

Blobrana

L

Posts: 131433

Date: May 14 15:42 2015

Galaxy star formation	Permalink

Galaxies die by slow 'strangulation' When galaxies stop making stars, their death is usually a slow process that chokes them of the necessary cool gases over about four billion years. That is the conclusion of astronomers who surveyed thousands of galaxies, living and dead, to assess whether the transition is rapid or slow. In the dead galaxies they detected high levels of metals, which build up during star formation and point to a slow strangulation process. Read more __________________

Blobrana

L

Posts: 131433

Date: May 14 08:56 2015

Galactic star formation	Permalink

Title: Strangulation as the primary mechanism for shutting down star formation in galaxies Author: Yingjie Peng, Roberto Maiolino, Rachel Cochrane Local galaxies are broadly divided into two main classes, star-forming (gas-rich) and quiescent (passive and gas-poor). The primary mechanism responsible for quenching star formation in galaxies and transforming them into quiescent and passive systems is still unclear. Sudden removal of gas through outflows or stripping is one of the mechanisms often proposed. An alternative mechanism is so-called "strangulation", in which the supply of cold gas to the galaxy is halted. Here we report that the difference between quiescent and star forming galaxies in terms of stellar metallicity (i.e. the fraction of metals heavier than helium in stellar atmospheres) can be used to discriminate efficiently between the two mechanisms. The analysis of the stellar metallicity in local galaxies, from 26,000 spectra, clearly reveals that strangulation is the primary mechanism responsible for quenching star formation, with a typical timescale of 4 billion years, at least for local galaxies with a stellar mass less than 10^11 solar masses. This result is further supported independently by the stellar age difference between quiescent and star-forming galaxies, which indicates that quiescent galaxies of less than 10^11 solar masses are on average observed four billion years after quenching due to strangulation. Read more (2458kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Feb 21 10:35 2014

Quenching of star formation	Permalink

Title: The Green Valley is a Red Herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early- and late-type galaxies Author: Kevin Schawinski, C. Megan Urry, Brooke D. Simmons, Lucy Fortson, Sugata Kaviraj, William C. Keel, Chris J. Lintott, Karen L. Masters, Robert C. Nichol, Marc Sarzi, Ramin, Skibba, Ezequiel Treister, Kyle W. Willett, O. Ivy Wong, Sukyoung K. Yi We use SDSS+GALEX+Galaxy Zoo data to study the quenching of star formation in low-redshift galaxies. We show that the green valley between the blue cloud of star-forming galaxies and the red sequence of quiescent galaxies in the colour-mass diagram is not a single transitional state through which most blue galaxies evolve into red galaxies. Rather, an analysis that takes morphology into account makes clear that only a small population of blue early-type galaxies move rapidly across the green valley after the morphologies are transformed from disk to spheroid and star formation is quenched rapidly. In contrast, the majority of blue star-forming galaxies have significant disks, and they retain their late-type morphologies as their star formation rates decline very slowly. We summarize a range of observations that lead to these conclusions, including UV-optical colours and halo masses, which both show a striking dependence on morphological type. We interpret these results in terms of the evolution of cosmic gas supply and gas reservoirs. We conclude that late-type galaxies are consistent with a scenario where the cosmic supply of gas is shut off, perhaps at a critical halo mass, followed by a slow exhaustion of the remaining gas over several Gyr, driven by secular and/or environmental processes. In contrast, early-type galaxies require a scenario where the gas supply and gas reservoir are destroyed virtually instantaneously, with rapid quenching accompanied by a morphological transformation from disk to spheroid. This gas reservoir destruction could be the consequence of a major merger, which in most cases transforms galaxies from disk to elliptical morphology, and mergers could play a role in inducing black hole accretion and possibly AGN feedback. Read more (4000kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Mar 17 01:19 2011

z=2-7 Star-Formation Plateau	Permalink

Title: On the puzzling plateau in the specific star formation rate at z=2-7 Authors: Simone M. Weinmann, Eyal Neistein, Avishai Dekel The observational indications for a constant specific star-formation rate (sSFR) in the redshift range z=2-7 are puzzling in the context of current galaxy-formation models. Despite the tentative nature of the data, their marked conflict with theory motivates a study of the possible implications. The plateau at sSFR ~ 2 Gyr^-1 is hard to reproduce because (a) its level is low compared to the cosmological specific accretion rate at z > 6, (b) it is higher than the latter at z ~ 2, (c) the natural correlation between SFR and stellar mass makes it difficult to manipulate their ratio, and (d) a low SFR at high z makes it hard to produce enough massive galaxies by z ~ 2. Using a flexible semi-analytic model, we explore ad-hoc modifications to the standard physical recipes trying to obey the puzzling observational constraints. Successful models involve non-trivial modifications, such as (a) a suppressed SFR at z > 4 in galaxies of all masses, by enhanced feedback or reduced SFR efficiency, following an initial active phase at z > 7, (b) a delayed gas consumption into stars, allowing the gas that was prohibited from forming stars or ejected at high z to form stars later in more massive galaxies, and (c) enhanced growth of massive galaxies, in terms of either faster assembly or more efficient starbursts in mergers, or by efficient star formation in massive haloes. Read more (1983kb, PDF) __________________

Page 1 of 1 sorted by

Create your own FREE Forum
Report Abuse