Abstract:

We present K-band imaging observations of ten gamma-ray burst (GRB) host galaxies for which an optical and/or radio afterglow associated with the GRB event was clearly identified. Data were obtained with the Very Large Telescope and New Technology Telescope at ESO (Chile), and with the Gemini-North telescope at Mauna Kea (Hawaii). Adding to our sample nine other GRB hosts with K-band photometry and determined redshifts published in the literature, we compare their observed and absolute K magnitudes as well as their R − K colours with those of other distant sources detected in various optical, nearinfrared, mid-infrared and submillimeter deep surveys. We find that the GRB host galaxies, most of them lying at 0.5 <∼ z <∼ 1.5, exhibit very blue colours, comparable to those of the faint blue star-forming sources at high redshift. They are sub-luminous in the K-band, suggesting a low stellar mass content. We do not find any GRB hosts harbouring R- and K-band properties similar to those characterizing the luminous infrared/submillimeter sources and the extremely red starbursts. Should GRBs be regarded as an unbiased probe of star-forming activity, this lack of luminous and/or reddened objects among the GRB host sample might reveal that the detection of GRB optical afterglows is likely biased toward unobscured galaxies. It would moreover support the idea that a large fraction of the optically-dark GRBs occur within dust-enshrouded regions of star formation. On the other hand, our result might also simply reflect intrinsic properties of GRB host galaxies experiencing a first episode of very massive star formation and characterized by a rather weak underlying stellar population. Finally, we compute the absolute B magnitudes for the whole sample of GRB host galaxies with known redshifts and detected at optical wavelengths. We find that the latter appear statistically even less luminous than the faint blue sources which mostly contributed to the B-band light emitted at high redshift. This indicates that the formation of GRBs could be favoured in particular systems with very low luminosities and, therefore, low metallicities. Such an intrinsic bias toward metal-poor environments would be actually consistent with what can be expected from the currently-favoured scenario of the “collapsar”. The forthcoming launch of the SWIFT mission at the end of 2003 will provide a dramatic increase of the number of GRB-selected sources. A detailed study of the chemical composition of the gas within this sample of galaxies will thus allow us to further analyse the potential effect of metallicity in the formation of GRB events.

Author affiliation: Le Floch, E.. CEA/DSM/DAPNIA Service d’Astrophysique; Francia

Author affiliation: Duc, P.. CEA/DSM/DAPNIA Service d’Astrophysique; Francia. Centre National de la Recherche Scientifique; Francia

Author affiliation: Mirabel Miquele, Igor Felix. CEA/DSM/DAPNIA Service d’Astrophysique; Francia. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina

Author affiliation: Sanders, D.. Max Planck Institut für Extraterrestrische Physik; Alemania

Author affiliation: Bosch, Guillermo Luis. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina

Author affiliation: Diaz, Ruben Joaquin. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina

Author affiliation: Donzelli, Carlos Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina

Author affiliation: Rodrigues, I.. CEA/DSM/DAPNIA Service d’Astrophysique; Francia

Author affiliation: Courvoisier, T.. INTEGRAL Science Data Center; Suiza

Author affiliation: Greiner, J.. Max Planck Institut für Extraterrestrische Physik; Alemania

Author affiliation: Mereghetti, S.. Istituto di Astrofisica Spaziale e Fisica Cosmica; Italia

Author affiliation: Melnick, J.. European Southern Observatory; Chile

Author affiliation: Maza, J.. Universidad de Chile; Chile

Author affiliation: Minitti, D.. Pontificia Universidad Católica de Chile; Chile

Abstract:

We present a new, detailed analysis of the morphologies and molecular gas fractions (MGFs) for a complete sample of 65 local luminous infrared galaxies from Great Observatories All-Sky Luminous Infrared Galaxies (LIRG) Survey using high resolution I-band images from The Hubble Space Telescope, the University of Hawaii 2.2 m Telescope and the Pan-STARRS1 Survey. Our classification scheme includes single undisturbed galaxies, minor mergers, and major mergers, with the latter divided into five distinct stages from pre-first pericenter passage to final nuclear coalescence. We find that major mergers of molecular gas-rich spirals clearly play a major role for all sources with ${L}_{\mathrm{IR}}\gt {10}^{11.5}{L}_{\odot };$ however, below this luminosity threshold, minor mergers and secular processes dominate. Additionally, galaxies do not reach ${L}_{\mathrm{IR}}\gt {10}^{12.0}{L}_{\odot }$ until late in the merger process when both disks are near final coalescence. The mean MGF ($\mathrm{MGF}\;=\;{M}_{{{\rm{H}}}_{2}}/({M}_{* }+{M}_{{{\rm{H}}}_{2}})$) for non-interacting and early-stage major merger LIRGs is 18 ± 2%, which increases to 33 ± 3%, for intermediate stage major merger LIRGs, consistent with the hypothesis that, during the early-mid stages of major mergers, most of the initial large reservoir of atomic gas (HI) at large galactocentric radii is swept inward where it is converted into molecular gas (H2).

Author affiliation: Larson, K. L.. University of Hawaii; Estados Unidos. California Institute of Technology; Estados Unidos

Author affiliation: Sanders, D. B.. Australian National University; Australia. University of Hawaii; Estados Unidos

Author affiliation: Barnes, J. E.. Kyoto University; Japón. University of Hawaii; Estados Unidos

Author affiliation: Ishida, C. M.. University of Hawaii; Estados Unidos

Author affiliation: Evans, A. S.. University of Virginia; Estados Unidos

Author affiliation: Mazzarella, J. M.. California Institute of Technology; Estados Unidos

Author affiliation: Kim, D. C.. National Radio Astronomy Observatory; Estados Unidos

Author affiliation: Privon, G. C.. Universidad de Concepción; Chile

Author affiliation: Mirabel Miquele, Igor Felix. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina

Author affiliation: Flewelling, H. A.. University of Hawaii; Estados Unidos

Abstract:

We present Very Large Telescope spectroscopic observations of the GRB 990705 host galaxy and highlight the benefits provided by the prompt phase features of gamma-ray bursts (GRBs) to derive the redshifts of the latter. In the host spectrum, we indeed detect an emission feature that we attribute to the [O II] λλ3726, 3729 doublet and derive an unambiguous redshift z = 0.8424 ± 0.0002 for this galaxy. This is in full agreement with the value z ∼ 0.86 ± 0.17 previously derived using a transient absorption edge discovered in the X-ray spectrum of GRB 990705. This burst is therefore the first GRB for which a reliable redshift was derived from the prompt phase emission itself, as opposed to redshift determinations performed using putative host galaxy emission lines or interstellar absorption lines in the GRB afterglows. Deep and high-resolution images of the host of GRB 990705 with the Space Telescope Imaging Spectrograph camera on board the Hubble Space Telescope reveal that the burst occurred in a nearly face-on Sc spiral galaxy typical of disk-dominated systems at 0.75 ≤ z ≤ 1. Assuming a cosmology with H<SUB>0</SUB> = 65 km s<SUP>-1</SUP> Mpc<SUP>-1</SUP>, Ω<SUB>m</SUB> = 0.3, and Ω<SUB>λ</SUB> = 0.7, we derive an absolute B magnitude M<SUB>B</SUB> = -21.75 for this galaxy and a star formation rate SFR ≈ 5-8 M⊙ yr<SUP>-1</SUP>. Finally, we discuss the implications of using X-ray transient features to derive GRB redshifts with larger burst samples and especially examine the case of short and dark long GRBs.

Facultad de Ciencias Astronómicas y Geofísicas