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.

Dynamical Properties of z ~ 2 Star-forming Galaxies and a Universal Star Formation Relation*

Abstract: We present the first comparison of the dynamical properties of different samples of z ~ 1.4-3.4 star-forming galaxies from spatially resolved imaging spectroscopy from SINFONI/VLT integral field spectroscopy and IRAM CO millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16 rest-frame optically selected, and 13 submillimeter galaxies (SMGs). We find that rest-frame UV and optically bright (K ranging from 0.06 to 0.2. In contrast, bright SMGs (S_(850) μm ≥ 5 mJy) have larger velocity widths and are much more compact. Hence, SMGs have lower angular momenta and higher matter densities than either the UV or optically selected populations. This indicates that dissipative major mergers may dominate the SMGs population, resulting in early spheroids, and that a significant fraction of the UV/optically bright galaxies have evolved less violently, either in a series of minor mergers, or in rapid dissipative collapse from the halo, given that either process may leads to the formation of early disks. These early disks may later evolve into spheroids via disk instabilities or mergers. Because of their small sizes and large densities, SMGs lie at the high surface density end of a universal (out to z = 2.5) "Schmidt-Kennicutt" relation between gas surface density and star formation rate surface density. The best-fit relation suggests that the star formation rate per unit area scales as the surface gas density to a power of ~1.7, and that the star formation efficiency increases by a factor of 4 between non-starbursts and strong starbursts.

Hubble space telescope and Spitzer imaging of red and blue galaxies at z 2.5: a correlation between size and star formation activity from compact quiescent galaxies to extended star-forming galaxies

Abstract: We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies at 2 < z < 3.5 in the FIRES MS 1054 field with red and blue rest-frame optical colors. About half of the galaxies are very compact (effective radii re < 1 kpc) at rest-frame optical wavelengths; the others are extended (1 kpc < re < 10 kpc). For reference, 1 kpc corresponds to 0.12'' at z = 2.5 in the adopted cosmology. We separate actively star-forming galaxies from quiescent galaxies by modeling their rest-frame UV-NIR SEDs. The star-forming galaxies span the full range of sizes, while the quiescent galaxies all have re < 2 kpc. In the redshift range where MIPS 24 ?m imaging is a sensitive probe of reradiated dust emission (z < 2.5), the 24 ?m fluxes confirm that the light of the small quiescent galaxies is dominated by old stars, rather than dust-enshrouded star formation or AGN activity. The inferred surface mass densities and velocity dispersions for the quiescent galaxies are very high compared to those in local galaxies. The galaxies follow a Kormendy relation (between surface brightness and size) with approximately the same slope as locally, but shifted to brighter surface brightnesses, consistent with a mean stellar formation redshift of zf ~ 5. This paper demonstrates a direct relation between star formation activity and size at z ~ 2.5 and the existence of a significant population of massive, extremely dense, old stellar systems without readily identifiable counterparts in the local universe.

SDSS IV MaNGA – spatially resolved diagnostic diagrams: a proof that many galaxies are LIERs

Abstract: We study the spatially resolved excitation properties of the ionised gas in a sample of 646 galaxies using integral field spectroscopy data from SDSS-IV MaNGA. Making use of Baldwin-Philips-Terlevich diagnostic diagrams we demonstrate the ubiquitous presence of extended (kpc scale) low ionisation emission-line regions (LIERs) in both star forming and quiescent galaxies. In star forming galaxies LIER emission can be associated with diffuse ionised gas, most evident as extra-planar emission in edge-on systems. In addition, we identify two main classes of galaxies displaying LIER emission: `central LIER' (cLIER) galaxies, where central LIER emission is spatially extended, but accompanied by star formation at larger galactocentric distances, and `extended LIER' (eLIER) galaxies, where LIER emission is extended throughout the whole galaxy. In eLIER and cLIER galaxies, LIER emission is associated with radially flat, low H$\alpha$ equivalent width of line emission ($

On the Nature of the NGC 1275 System

Abstract: Subarcsecond images, taken in B, R, and Hα filters, and area spectroscopy obtained with the WIYN 3.5 m telescope provide the basis for an investigation of the unusual structures in the stellar body and ionized gas in and around the Perseus Cluster central galaxy NGC 1275. Our Hα filter is tuned to gas at the velocity of NGC 1275, revealing complex, probably unresolved, small-scale features in the extended ionized gas, located up to 50 h kpc from NGC 1275. The mean Hα surface brightness varies little along the outer filaments; this, together with the complex excitation state demonstrated by spectra, imply that the filaments are likely to be tubes, or ribbons, of gas. The morphology, location, and inferred physical parameters of the gas in the filaments are consistent with a model, whereby the filaments form through compression of the intracluster gas by relativistic plasma emitted from the active nucleus of NGC 1275. Imaging spectroscopy with the DensePak fiber array on WIYN suggests partial rotational support of the inner component of low-velocity ionized gas. Our broadband data is used to derive color maps of the stellar distribution and also to investigate asymmetries in the stellar surface brightness. We confirm and extend evidence for features in the stellar body of NGC 1275 and identify outer stellar regions containing very blue, probably very young, star clusters. We interpret these as evidence for recent accretion of a gas-rich system, with subsequent star formation. Other star clusters are identified, some of which are possibly associated with the high-velocity 8200 km s-1 emission-line system being in the same projected location. We suggest that two main processes, which may be causally connected, are responsible for the rich phenomenology of the NGC 1275 system—NGC 1275 experienced a recent merger and/or interaction with a group of gas-rich galaxies, and recent outflows from its AGN have compressed the intracluster gas and perhaps the gas in the infalling galaxies to produce a complex web of filaments.

NIHAO project – I. Reproducing the inefficiency of galaxy formation across cosmic time with a large sample of cosmological hydrodynamical simulations

Abstract: We introduce project NIHAO (Numerical Investigation of a Hundred Astrophysical Objects), a set of 100 cosmological zoom-in hydrodynamical simulations performed using the GASOLINE code, with an improved implementation of the SPH algorithm. The haloes in our study range from dwarf (M-200 similar to 5 x 10(9) M-circle dot) to Milky Way (M-200 similar to 2 x 10(12) M-circle dot) masses, and represent an unbiased sampling of merger histories, concentrations and spin parameters. The particle masses and force softenings are chosen to resolve the mass profile to below 1 per cent of the virial radius at all masses, ensuring that galaxy half-light radii are well resolved. Using the same treatment of star formation and stellar feedback for every object, the simulated galaxies reproduce the observed inefficiency of galaxy formation across cosmic time as expressed through the stellar mass versus halo mass relation, and the star formation rate versus stellar mass relation. We thus conclude that stellar feedback is the chief piece of physics required to limit the efficiency of star formation in galaxies less massive than the Milky Way.