J/ApJ/802/103 Model predictions for GRB host galaxies (Trenti+, 2015) ================================================================================ The luminosity and stellar mass functions of GRB host galaxies: insight into the metallicity bias. Trenti M., Perna R., Jimenez R. =2015ApJ...802..103T ================================================================================ ADC_Keywords: Gamma rays ; Redshifts ; Stars, masses ; Abundances Keywords: galaxies: general; galaxies: high-redshift; gamma-ray burst: general; stars: formation Abstract: Long-duration gamma-ray bursts (GRBs) are powerful probes of the star formation history of the universe, but the correlation between the two depends on the highly debated presence and 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 and apply it to GRB production. We predict the luminosities, stellar masses, and metallicities of host galaxies depending on the presence (or absence) of a metallicity bias. Our best-fitting model includes a moderate metallicity bias, broadly consistent with the large majority of the long-duration GRBs in metal-poor environments originating from a collapsar (probability ~83%, with [0.74;0.91] range at 90% confidence level), but with a secondary contribution (~17%) from a metal-independent production channel, 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 (z>~2), 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 data sets, and suggests that lower efficiencies of the metal-independent GRB channel might be preferred following a comprehensive fit that includes metallicity of GRB hosts from complete samples. Overall, we are able to clearly establish the presence of a metallicity bias for GRB production, but continued characterization of GRB host galaxies is needed to quantify its strength. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 106 46836 Model predictions for GRB host properties -------------------------------------------------------------------------------- See also: J/ApJ/778/128 : GRB-host galaxies photometry (Perley+, 2013) J/A+A/556/A55 : Multi-color photometry of star-forming galaxies (Ilbert+, 2013) J/ApJ/683/321 : Metallicities of GRB, DLA, and Ly{alpha} galaxies (Fynbo+, 208) Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 E12.6 --- z [0.25/9] Model redshift 14- 25 E12.6 --- p [1e-11/10000] Model plateau value (1) 27- 39 E13.6 mag Mag.d [-25.8/-10.9] GRB host galaxy absolute UV magnitude, including dust extinction (AB scale) 41- 53 E13.6 mag Mag [-28/-11] GRB intrinsic host galaxy absolute UV magnitude M_UV_ (AB scale) 55- 66 E12.6 Msun M* [181894/4.5662e+11] GRB host galaxy stellar mass 68- 79 E12.6 Msun Mdm GRB host galaxy dark-matter halo mass 81- 93 E13.6 [Sun] logZ [-4.8/0.4] Log Metallicity log_10_(Z/Z_{sun}_) 95-106 E12.6 --- N Cumulative number of GRBs in hosts having magnitude<=M_UV_ (1) -------------------------------------------------------------------------------- Note (1): The normalization for the cumulative distribution is such that for a given value of p (value for the efficiency of forming GRBs), the z=3.75 model has cumulative number of GRBs defined as unity for M_AB_=-11.0. Other redshift values use the same normalization, so for example it is immediate to derive the comoving GRB rate at redshift z relative to redshift z=3.75, at fixed p, since it is simply column 8 of the last line of each group. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 24-Jul-2015