Star formation

About: Star formation is a research topic. Over the lifetime, 37405 publications have been published within this topic receiving 1808161 citations. The topic is also known as: astrogenesis.

The many manifestations of downsizing: hierarchical galaxy formation models confront observations

Abstract: It has been widely claimed that several lines of observational evidence point towards a ‘downsizing’ of the process of galaxy formation over cosmic time. This behaviour is sometimes termed ‘antihierarchical’, and contrasted with the ‘bottom-up’ (small objects form first) assembly of the dark matter structures in cold dark matter (CDM) models. In this paper, we address three different kinds of observational evidence that have been described as ‘downsizing’: the stellar mass assembly (i.e. more massive galaxies assemble at higher redshift with respect to low-mass ones), star formation rate (SFR) (i.e. the decline of the specific star formation rate is faster for more massive systems) and the ages of the stellar populations in local galaxies (i.e. more massive galaxies host older stellar populations). We compare a broad compilation of available data sets with the predictions of three different semi-analytic models

Baryons matter: why luminous satellite galaxies have reduced central masses

Abstract: Using high-resolution cosmological hydrodynamical simulations of Milky Way-massed disk galaxies, we demonstrate that supernovae feedback and tidal stripping lower the central masses of bright (–15 < MV < –8) satellite galaxies. These simulations resolve high-density regions, comparable to giant molecular clouds, where stars form. This resolution allows us to adopt a prescription for H2 formation and destruction that ties star formation to the presence of shielded, molecular gas. Before infall, supernova feedback from the clumpy, bursty star formation captured by this physically motivated model leads to reduced dark matter (DM) densities and shallower inner density profiles in the massive satellite progenitors (M vir ≥ 109 M ☉, M * ≥ 107 M ☉) compared with DM-only simulations. The progenitors of the lower mass satellites are unable to maintain bursty star formation histories, due to both heating at reionization and gas loss from initial star-forming events, preserving the steep inner density profile predicted by DM-only simulations. After infall, gas stripping from satellites reduces the total central masses of satellites simulated with DM+baryons relative to DM-only satellites. Additionally, enhanced tidal stripping after infall due to the baryonic disk acts to further reduce the central DM densities of the luminous satellites. Satellites that enter with cored DM halos are particularly vulnerable to the tidal effects of the disk, exacerbating the discrepancy in the central masses predicted by baryon+DM and DM-only simulations. We show that DM-only simulations, which neglect the highly non-adiabatic evolution of baryons described in this work, produce denser satellites with larger central velocities. We provide a simple correction to the central DM mass predicted for satellites by DM-only simulations. We conclude that DM-only simulations should be used with great caution when interpreting kinematic observations of the Milky Way's dwarf satellites.

T Tauri Stars: Wild as Dust

Abstract: Les similarites et les differences entre les etoiles T Tauri et les etoiles de masses comparables durant leurs evolutions sont etudiees a partir d'etudes preexistantes

H I, H II, and R-Band Observations of a Galactic Merger Sequence

Abstract: We present high-quality aperture synthesis observations of the neutral hydrogen distribution in a sample of five galactic systems believed to be involved in progressive stages of merging: Arp295, NGC4676, NGC520, NGC3921, and NGC7252. These data are supplemented by wide-field images taken through a narrow band Halpha filter, and by deep R-band surface photometry. In the early stages, large amounts of HI exist within the galactic disks and star formation is widespread. The ionized gas emission often takes on the appearance of plumes and arcs emanating from the nuclear regions, which are presumably the sites of interaction induced starbursts. In the final stages there is little if any HI within the remnant bodies, and tidal material is seen moving inward. This suggests that these remnants will evolve into elliptical galaxies in their atomic gas contents as well as their photometric properties. However the observations of NGC520 reveal an extensive rotating gaseous disk, suggesting that perhaps some mergers will not destroy the atomic gas disks of the progenitors. Overall, large quantities of both gas and starlight are seen at large radii. Since this material evolves on very long time scales, it may leave observable signatures for many Gyr.

Two bright submillimeter galaxies in a z=4.05 proto-cluster in GOODS-North, and accurate radio-infrared photometric redshifts

Abstract: We present the serendipitous discovery of z=4.05 molecular gas CO emission lines with the IRAM Plateau de Bure interferometer coincident with GN20 and GN20.2, two luminous submillimeter galaxies (SMGs) in the Great Observatories Origins Deep Survey North field (GOODS-N). These are among the most distant submillimeter-selected galaxies reliably identified through CO emission and also some of the most luminous known. In terms of CO to bolometric luminosities, stellar mass and star formation rates (SFRs), these newly discovered z>4 SMGs are similar to z~1.5-3 SMGs studied to date. These z~4 SMGs have much higher specific SFRs than typical B-band dropout Lyman break galaxies at the same redshift. The stellar mass-SFR correlation for normal galaxies does not seem to evolve much further, between z~2 and z~4. A significant z=4.05 spectroscopic redshift spike is observed in GOODS-N, and a strong spatial overdensity of B-band dropouts and IRAC selected z>3.5 galaxies appears to be centered on the GN20 and GN20.2 galaxies. This suggests a proto-cluster structure with total mass ~10^14 Msun. Using photometry at mid-IR, submm and radio wavelengths, we show that reliable photometric redshifts (Dz/(1+z)~0.1) can be derived for SMGs over 1 3.5 starbursts, regardless of their submm/mm emission [abridged].