Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userBalancing the Energy Budget: Star-Formation versus AGN in High Redshift Infrared Luminous Galaxies
158
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present deep {it Spitzer} mid-infrared spectroscopy, along with 16, 24, 70, and 850,$micron$ photometry, for 22 galaxies located in the Great Observatories Origins Deep Survey-North (GOODS-N) field. The sample spans a redshift range of $0.6la z la 2.6$, 24~$mu$m flux densities between $sim$0.2$-$1.2 mJy, and consists of submillimeter galaxies (SMGs), X-ray or optically selected active galactic nuclei (AGN), and optically faint ($z_{AB}>25$,mag) sources. We find that infrared (IR; $8-1000~micron$) luminosities derived by fitting local spectral energy distributions (SEDs) with 24~$micron$ photometry alone are well matched to those when additional mid-infrared spectroscopic and longer wavelength photometric data is used for galaxies having $zla1.4$ and 24~$micron$-derived IR luminosities typically $la 3times 10^{12}~L_{sun}$. However, for galaxies in the redshift range between $1.4la z la 2.6$, typically having 24~$micron$-derived IR luminosities $ga 3times 10^{12}~L_{sun}$, IR luminosities are overestimated by an average factor of $sim$5 when SED fitting with 24~$micron$ photometry alone. This result arises partly due to the fact that high redshift galaxies exhibit aromatic feature equivalent widths that are large compared to local galaxies of similar luminosities. Through a spectral decomposition of mid-infrared spectroscopic data, we are able to isolate the fraction of IR luminosity arising from an AGN as opposed to star formation activity. This fraction is only able to account for $sim$30% of the total IR luminosity among the entire sample.
rate research
Read More
The enormous amounts of infrared (IR) radiation emitted by luminous infrared galaxies (LIRGs, L_IR=10^11-10^12Lsun) and ultraluminous infrared galaxies (ULIRGs, L_IR>10^12Lsun) are produced by dust heated by intense star formation (SF) activity and/or an active galactic nucleus (AGN). The elevated star formation rates and high AGN incidence in (U)LIRGs make them ideal candidates to study the interplay between SF and AGN activity in the local universe. In this paper I review recent results on the physical extent of the SF activity, the AGN detection rate (including buried AGN), the AGN bolometric contribution to the luminosity of the systems, as well as the evolution of local LIRGs and ULIRGs. The main emphasis of this review is on recent results from IR observations.
I present a model for the star formation properties of z~2 starburst galaxies. Here, I discuss models for the formation of high-z Submillimeter Galaxies, as well as the CO-H2 conversion factor for these systems. I then apply these models to literature observations. I show that when using a functional form for XCO that varies smoothly with the physical properties in galaxies, galaxies at both local and high-z lie on a unimodal Kennicutt-Schmidt star formation law, with power-law index of ~2. The inferred gas fractions of these galaxies are large (fgas ~ 0.2-0.4), though a factor ~2 lower than most literature estimates that utilize locally-calibrated CO-H2 conversion factors.
We study the star formation and the mass assembly process of 0.3<=z<2.5 galaxies using their IR emission from MIPS 24um band. We used an updated version of the GOODS-MUSIC catalog, extended by the addition of mid-IR fluxes. We compared two different estimators of the Star Formation Rate: the total infrared emission derived from 24um, estimated using both synthetic and empirical IR templates, and the multiwavelength fit to the full galaxy SED. For both estimates, we computed the SFR Density and the Specific SFR. The two SFR tracers are roughly consistent, given the uncertainties involved. However, they show a systematic trend, IR-based estimates exceeding the fit-based ones as the SFR increases. We show that: a) at z>0.3, the SFR is well correlated with stellar mass, and this relationship seems to steepen with redshift (using IR-based SFRs); b) the contribution to the global SFRD by massive galaxies increases with redshift up to ~2.5, more rapidly than for galaxies of lower mass, but appears to flatten at higher z; c) despite this increase, the most important contributors to the SFRD at any z are galaxies of about, or immediately lower than, the characteristic stellar mass; d) at z~2, massive galaxies are actively star-forming, with a median SFR 300 Msun/yr. During this epoch, they assemble a substantial part of their final stellar mass; e) the SSFR shows a clear bimodal distribution. The analysis of the SFRD and the SSFR seems to support the downsizing scenario, according to which high mass galaxies have formed their stars earlier and faster than their low mass counterparts. A comparison with theoretical models indicates that they follow the global increase in the SSFR with redshift and predict the existence of quiescent galaxies even at z>1.5, but they systematically underpredict the average SSFR.
We propose that star formation is delayed relative to the inflow rate in rapidly-accreting galaxies at very high redshift (z > 2) because of the energy conveyed by the accreting gas. Accreting gas streams provide fuel for star formation, but they stir the disk and increase turbulence above the usual levels compatible with gravitational instability, reducing the star formation efficiency in the available gas. After the specific inflow rate has sufficiently decreased - typically at z < 3 - galaxies settle in a self-regulated regime with efficient star formation. An analytic model shows that this interaction between infalling gas and young galaxies can significantly delay star formation and maintain high gas fractions (>40%) down to z = 2, in contrast to other galaxy formation models. Idealized hydrodynamic simulations of infalling gas streams onto primordial galaxies confirm the efficient energetic coupling at z > 2, and suggest that this effect is largely under-resolved in existing cosmological simulations.
The observational study of star formation relations in galaxies is central to unraveling the physical processes at work on local and global scales. We wish to expand the sample of extreme starbursts, represented by local LIRGs and ULIRGs, with high quality observations in the 1-0 line of HCN. We study if a universal law can account for the star formation relations observed for the dense molecular gas in normal star forming galaxies and extreme starbursts. We have used the IRAM 30m telescope to observe a sample of 19 LIRGs in the 1-0 lines of CO, HCN and HCO+. The analysis of the new data proves that the efficiency of star formation in the dense molecular gas (SFE-dense) of extreme starbursts is a factor 3-4 higher compared to normal galaxies. We find a duality in Kennicutt-Schmidt (KS) laws that is reinforced if we account for the different conversion factor for HCN (alpha-HCN) in extreme starbursts and for the unobscured star formation rate in normal galaxies. This result extends to the higher molecular densities probed by HCN lines the more extreme bimodal behavior of star formation laws, derived from CO molecular lines by two recent surveys. We have confronted our observations with the predictions of theoretical models in which the efficiency of star formation is determined by the ratio of a constant star formation rate per free-fall time (SFR-ff) to the local free-fall time. We find that it is possible to fit the observed differences in the SFE-dense between normal galaxies and LIRGs/ULIRGs using a common constant SFR-ff and a set of physically acceptable HCN densities, but only if SFR-ff~0.005-0.01 and/or if alpha-HCN is a factor of a few lower than our favored values. Star formation recipes that explicitly depend on the galaxy global dynamical time scales do not significantly improve the fit to the new HCN data presented in this work.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
