The longγ-ray burst rate and the correlation with host galaxy properties

Abstract

Context. To answer questions on the start and duration of the epoch of reionisation, periods of galaxy mergers and properties of other cosmological encounters, the cosmic star formation history,ρ * or CSFH, is of fundamental importance. Using the association of long-duration gamma-ray bursts (LGRBs) with the death of massive stars and their ultra-luminous nature (>10 52 erg s −1 ), the CSFH can be probed to higher redshifts than current conventional methods. Unfortunately, no consensus has been reached on the manner in which the LGRB rate,ρ grb or LGRBR, traces the CSFH, leaving many of the questions mentioned mostly unexplored by this method. Aims. Observations by the gamma-ray burst near-infrared detector (GROND) over the past 4 years have, for the first time, acquired highly complete LGRB samples. Driven by these completeness levels and new evidence of LGRBs also occurring in more massive and metal rich galaxies than previously thought, the possible biases of theρ grb -ρ * connection are investigated over a large range of galaxy properties. Methods. The CSFH is modelled using empirical fits to the galaxy mass function and galaxy star formation rates. Biasing the CSFH by means of metallicity cuts, mass range boundaries, and other unknown redshift dependencies of the formρ grb ∝ρ * (1 + z) δ , aρ grb is generated and compared to the highly complete GROND LGRB sample. Results. It is found that there is no strong preference for a metallicity cut or fixed galaxy mass boundaries and that there are no unknown redshift effects (δ = 0), in contrast to previous work which suggest values of Z/Z ∼ 0.1−0.3. From the best-fit models obtained, we predict that ∼1.2% of the LGRB burst sample exists above z = 6. Conclusions. The linear relationship betweenρ grb andρ * suggested by our results implies that redshift biases present in previous LGRB samples significantly affect the inferred dependencies of LGRBs on their host galaxy properties. Such biases can lead to, for example, an interpretation of metallicity limitations and evolving LGRB luminosity functions.

The First Billion Years project: gamma-ray bursts at z > 5

“…Early studies showed an overabundance of LGRBs at higher redshifts than that inferred from the CSFH (e.g., Daigne, Rossi & Mochkovitch 2006). This underlying excess has been explained for many different reasons ranging from observational biases (Coward et al 2008;Elliott et al 2012) to redshift-dependent initial mass functions (IMF; Wang & Dai 2011). However, the most favoured explanation is a metallicity dependence that is driven by (i) the requirement of the single progenitor collapsar model, and (ii) LGRB host galaxy observations (see, e.g., Le Floc'h et al 2003;Savaglio, Glazebrook & Le Borgne 2009;Svensson et al 2010;Mannucci, Salvaterra & Campisi 2011).…”

“…This has lead many authors to investigate the differences, if any, between the LGRB rate and the cosmic star formation history (CSFH; e.g., Wijers et al 1998;Bromm & Loeb 2006;Daigne, Rossi & Mochkovitch 2006;Li 2008;Butler, Bloom & Poznanski 2010;Wanderman & Piran 2010;Elliott et al 2012). Early studies showed an overabundance of LGRBs at higher redshifts than that inferred from the CSFH (e.g., Daigne, Rossi & Mochkovitch 2006).…”

“…The first results obtained on host galaxy samples showed that they were primarily blue with lowmass, and low-metallicity (e.g., Fruchter et al 1999;Le Floc'h et al 2003;Berger et al 2003;Christensen, Hjorth & Gorosabel 2004;Tanvir et al 2004;Savaglio, Glazebrook & Le Borgne 2009) and suggested that the metallicity of the host could be a proxy for the progenitor. Such proxies exerted a strict metallicity-cut (e.g., Langer & Norman 2006;Salvaterra & Chincarini 2007;Butler, Bloom & Poznanski 2010;Elliott et al 2012), such that only host galaxies below a given value could host a LGRB, which lead to predictions that the CSFH flattens at higher redshifts (e.g., Kistler et al 2009;Salvaterra et al 2012). However, these host galaxy studies were optically biased, which when accounted for, systematically more massive galaxies were found (e.g., Krühler et al 2011;Rossi et al 2012).…”

“…The GROND upper limit 2 sample (outlined in Elliott et al 2012) has a redshift completeness of 95% and has a redshift range z = 0 − 12. The number density is calculated by taking the histogram of the sample and dividing each bin by its size and redshift volume.…”

Research on the redshift evolution of luminosity function and selection effect of GRBs

“…Furthermore, Yu et al (2015) even found an excess of GRB rate at low redshift of z < 1.0 (see also Petrosian et al 2015). Many theoretical models have been proposed to explain the discrepancy between the GRB rate and SFR, e.g., the evolution of the cosmic metallicity (Langer & Norman 2006;Li 2008;Elliott et al 2012), the evolution of the initial mass function (Wang & Dai 2011), or the additional cosmic string explosions (Cheng et al 2010). However, most previous works are based on the assumption that the luminosity function (LF) is a constant form and independent of redshift.…”