Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe luminosity and stellar mass functions of GRB host galaxies: Insight into the metallicity bias
111
0
0.0
(
0
)
Authors
Michele Trenti
Ask ChatGPT about the research
No Arabic abstract
Long-Duration Gamma-Ray Bursts (GRBs) are powerful probes of the Universe star formation history, but correlation between the two depends on the highly debated presence/strength of a metallicity bias. To investigate this correlation, we use a phenomenological model that successfully describes star formation rates, luminosities and stellar masses of star forming galaxies, applying it to GRB production. We predict luminosities, stellar masses, and metallicities of host galaxies depending on the metallicity bias. Our best-fitting model includes a moderate metallicity bias, broadly consistent with the large majority of long-duration GRBs in metal-poor environments originating from collapsars (probability ~83%), but with a secondary contribution (~17%) from metal-independent production channels, such as binary evolution. Because of the mass-metallicity relation of galaxies, the maximum likelihood model predicts that the metal-independent channel becomes dominant at z<2, where hosts have higher metallicities and collapsars are suppressed. This possibly explains why some studies find no clear evidence of a metal-bias based on low-z samples. However, while metallicity predictions match observations well at high redshift, there is tension with low redshift observations, since a significant fraction of GRB hosts are predicted to have (near-)solar metallicity. This is in contrast to observations, unless obscured, metal-rich hosts are preferentially missed in current datasets, and suggests that lower efficiencies of the metal-independent GRB channel might be preferred following a comprehensive fit from complete samples. Overall, we are able to establish the presence of a metallicity bias for GRB production, but continued characterization of GRB host galaxies is needed to quantify its strength.
rate research
Read More
We investigate the nature of the mass-metallicity (M-Z) relation for long gamma-ray burst (LGRB) host galaxies. Recent studies suggest that the M-Z relation for local LGRB host galaxies may be systematically offset towards lower metallicities relative to the M-Z relation defined by the general star forming galaxy (SDSS) population. The nature of this offset is consistent with suggestions that low metallicity environments may be required to produce high mass progenitors, although the detection of several GRBs in high-mass, high-metallicity galaxies challenges the notion of a strict metallicity cut-off for host galaxies that are capable of producing GRBs. We show that the nature of this reported offset may be explained by a recently proposed anti-correlation between the star formation rate (SFR) and the metallicity of star forming galaxies. If low metallicity galaxies produce more stars than their equally massive, high-metallicity counterparts, then transient events that closely trace the SFR in a galaxy would be more likely to be found in these low metallicity, low mass galaxies. Therefore, the offset between the GRB and SDSS defined M-Z relations may be the result of the different methods used to select their respective galaxy populations, with GRBs being biased towards low metallicity, high SFR, galaxies. We predict that such an offset should not be expected of transient events that do not closely follow the star formation history of their host galaxies, such as short duration GRBs and SN Ia, but should be evident in core collapse SNe found through upcoming untargeted surveys.
We present the results of the analysis of deep photometric data of 32 Galactic globular clusters. We analysed 69 parallel field images observed with the Wide Field Channel of the Advanced Camera for Surveys of the Hubble Space Telescope which complemented the already available photometry from the globular cluster treasury project covering the central regions of these clusters. This unprecedented data set has been used to calculate the relative fraction of stars at different masses (i.e. the present-day mass function) in these clusters by comparing the observed distribution of stars along the cluster main sequence and across the analysed field of view with the prediction of multimass dynamical models. For a subsample of 31 clusters, we were able to obtain also the half-mass radii, mass-to-light ratios and the mass fraction of dark remnants using available radial velocity information. We found that the majority of globular clusters have single power law mass functions $F(m) propto m^alpha$ with slopes $alpha>-1$ in the mass range $0.2<m/text{M}_{odot}<0.8$. By exploring the correlations between the structural/dynamical and orbital parameters, we confirm the tight anticorrelation between the mass function slopes and the half-mass relaxation times already reported in previous works, and possible second-order dependence on the cluster metallicity. This might indicate the relative importance of both initial conditions and evolutionary effects on the present-day shape of the mass function.
We try to identify the nature of high redshift long Gamma-Ray Bursts (LGRBs) host galaxies by comparing the observed abundance ratios in the interstellar medium with detailed chemical evolution models accounting for the presence of dust. We compared measured abundance data from LGRB afterglow spectra to abundance patterns as predicted by our models for different galaxy types. We analysed in particular [X/Fe] abundance ratios (where X is C, N, O, Mg, Si, S, Ni, Zn) as functions of [Fe/H]. Different galaxies (irregulars, spirals, ellipticals) are, in fact, characterised by different star formation histories, which produce different [X/Fe] ratios (time-delay model). This allows us to identify the morphology of the hosts and to infer their age (i.e. the time elapsed from the beginning of star formation) at the time of the GRB events, as well as other important parameters. Relative to previous works, we use newer models in which we adopt updated stellar yields and prescriptions for dust production, accretion and destruction. We have considered a sample of seven LGRB host galaxies. Our results have suggested that two of them (GRB 050820, GRB 120815A) are ellipticals, two (GRB 081008, GRB 161023A) are spirals and three (GRB 050730, GRB 090926A, GRB 120327A) are irregulars. We also found that in some cases changing the initial mass function can give better agreement with the observed data. The calculated ages of the host galaxies span from the order of 10 Myr to little more than 1 Gyr.
We present a suite of cosmological zoom-in simulations at z>5 from the Feedback In Realistic Environments project, spanning a halo mass range M_halo~10^8-10^12 M_sun at z=5. We predict the stellar mass-halo mass relation, stellar mass function, and luminosity function in several bands from z=5-12. The median stellar mass-halo mass relation does not evolve strongly at z=5-12. The faint-end slope of the luminosity function steepens with increasing redshift, as inherited from the halo mass function at these redshifts. Below z~6, the stellar mass function and ultraviolet (UV) luminosity function slightly flatten below M_star~10^4.5 M_sun (fainter than M_1500~-12), owing to the fact that star formation in low-mass halos is suppressed by the ionizing background by the end of reionization. Such flattening does not appear at higher redshifts. We provide redshift-dependent fitting functions for the SFR-M_halo, SFR-M_star, and broad-band magnitude-stellar mass relations. We derive the star formation rate density and stellar mass density at z=5-12 and show that the contribution from very faint galaxies becomes more important at z>8. Furthermore, we find that the decline in the z~6 UV luminosity function brighter than M_1500~-20 is largely due to dust attenuation. Approximately 37% (54%) of the UV luminosity from galaxies brighter than M_1500=-13 (-17) is obscured by dust at z~6. Our results broadly agree with current data and can be tested by future observations.
We present direct constraints on how the formation of low-mass X-ray binary (LMXB) populations in galactic fields depends on stellar age. In this pilot study, we utilize Chandra and Hubble Space Telescope (HST) data to detect and characterize the X-ray point source populations of three nearby early-type galaxies: NGC 3115, 3379, and 3384. The luminosity-weighted stellar ages of our sample span 3-10 Gyr. X-ray binary population synthesis models predict that the field LMXBs associated with younger stellar populations should be more numerous and luminous per unit stellar mass than older populations due to the evolution of LMXB donor star masses. Crucially, the combination of deep Chandra and HST observations allows us to test directly this prediction by identifying and removing counterparts to X-ray point sources that are unrelated to the field LMXB populations, including LMXBs that are formed dynamically in globular clusters, Galactic stars, and background AGN/galaxies. We find that the young early-type galaxy NGC 3384 (~2-5 Gyr) has an excess of luminous field LMXBs (L_X > (5-10) x 10^37 erg/s) per unit K-band luminosity (L_K; a proxy for stellar mass) than the old early-type galaxies NGC 3115 and 3379 (~8-10 Gyr), which results in a factor of ~2-3 excess of LX/LK for NGC 3384. This result is consistent with the X-ray binary population synthesis model predictions; however, our small galaxy sample size does not allow us to draw definitive conclusions on the evolution field LMXBs in general. We discuss how future surveys of larger galaxy samples that combine deep Chandra and HST data could provide a powerful new benchmark for calibrating X-ray binary population synthesis models.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
