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Register a new userThe nature of GRB-selected submillimeter galaxies: hot and young
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Micha{\\l} Jerzy Micha{\\l}owski
Publication date
2007
fields
Physics
and research's language is
English
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We present detailed fits of the spectral energy distributions (SEDs) of four submillimeter (submm) galaxies selected by the presence of a gamma-ray burst (GRB) event (GRBs 980703, 000210, 000418 and 010222). These faint ~3 mJy submm emitters at redshift ~1 are characterized by an unusual combination of long- and short-wavelength properties, namely enhanced submm and/or radio emission combined with optical faintness and blue colors. We exclude an active galactic nucleus as the source of long-wavelength emission. From the SED fits we conclude that the four galaxies are young (ages <2 Gyr), highly starforming (star formation rates ~150 MSun/yr), low-mass (stellar masses ~10^10 MSun) and dusty (dust masses ~3x10^8 MSun). Their high dust temperatures (Td>45 K) indicate that GRB host galaxies are hotter, younger, and less massive counterparts to submm-selected galaxies detected so far. Future facilities like Herschel, JCMT/SCUBA-2 and ALMA will test this hypothesis enabling measurement of dust temperatures of fainter GRB-selected galaxies.
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Using detailed spectral energy distribution fits we present evidence that submillimeter- and radio-bright gamma-ray burst host galaxies are hotter counterparts to submillimeter galaxies. This hypothesis makes them of special interest since hotter submm galaxies are difficult to find and are believed to contribute significantly to the star formation history of the Universe.
We report on deep near-infrared (NIR) observations of submillimeter-selected galaxies (SMGs) with the Near Infrared Camera (NIRC) on the Keck I telescope. We have identified K-band candidate counterparts for 12 out of 15 sources in the SCUBA Cluster Lens Survey. Three SMGs remain non-detections with K-band limits of K>23 mag, corrected for lensing. Compensating for lensing we find a median magnitude of K=22+/-1 mag for the SMG population, but the range of NIR flux densities spans more than a factor of 400. For SMGs with confirmed counterparts based on accurate positions from radio, CO, and/or millimeter continuum interferometric observations, the median NIR color is J-K=2.6+/-0.6 mag. The NIR-bright SMGs (K<19 mag) have colors of J-K =~ 2 mag, while the faint SMGs tend to be extremely red in the NIR (J-K>3 mag). We argue that a color selection criterion of J-K>~3 mag can be used to help identify counterparts of SMGs that are undetected at optical and radio wavelengths. The number density of sources with J-K>3 mag is 5 arcmin^{-2} at K<22.5 mag, greater than that of SMGs with S(850um)>2 mJy. It is not clear if the excess represents less luminous infrared-bright galaxies with S(850um)<~2 mJy, or if the faint extremely red NIR galaxies represent a different population of sources that could be spatially related to the SMGs.
We have used the Caltech Submillimeter Observatory (CSO) to follow-up a sample of WISE-selected, hyperluminous galaxies, so called W1W2-dropout galaxies. This is a rare (~ 1000 all-sky) population of galaxies at high redshift (peaks at z=2-3), that are faint or undetected by WISE at 3.4 and 4.6 um, yet are clearly detected at 12 and 22 um. The optical spectra of most of these galaxies show significant AGN activity. We observed 14 high-redshift (z > 1.7) W1W2-dropout galaxies with SHARC-II at 350 to 850 um, with 9 detections; and observed 18 with Bolocam at 1.1 mm, with five detections. Warm Spitzer follow-up of 25 targets at 3.6 and 4.5 um, as well as optical spectra of 12 targets are also presented in the paper. Combining WISE data with observations from warm Spitzer and CSO, we constructed their mid-IR to millimeter spectral energy distributions (SEDs). These SEDs have a consistent shape, showing significantly higher mid-IR to submm ratios than other galaxy templates, suggesting a hotter dust temperature. We estimate their dust temperatures to be 60-120 K using a single-temperature model. Their infrared luminosities are well over 10^{13} Lsun. These SEDs are not well fitted with existing galaxy templates, suggesting they are a new population with very high luminosity and hot dust. They are likely among the most luminous galaxies in the Universe. We argue that they are extreme cases of luminous, hot dust-obscured galaxies (DOGs), possibly representing a short evolutionary phase during galaxy merging and evolution. A better understanding of their long-wavelength properties needs ALMA as well as Herschel data.
We use deep far-IR, submm, radio and X-ray imaging and mid-IR spectroscopy to explore the nature of a sample of Spitzer-selected dust-obscured galaxies (DOGs) in GOODS-N. A sample of 79 galaxies satisfy the criteria R-[24]>14 (Vega) down to S24>100 microJy. Twelve of these galaxies have IRS spectra available which we use to measure redshifts and classify these objects as being dominated by star formation or active galactic nuclei (AGN) activity in the mid-IR. The IRS spectra and Spitzer photometric redshifts confirm that the DOGs lie in a tight redshift distribution around z~2. Based on mid-IR colors, 80% of DOGs are likely dominated by star formation; the stacked X-ray emission from this sub-sample of DOGs is also consistent with star formation. Since only a small number of DOGs are individually detected at far-IR and submm wavelengths, we use a stacking analysis to determine the average flux from these objects and plot a composite IR (8-1000 microns) spectral energy distribution (SED). The average luminosity of these star forming DOGs is LIR~1e12 Lsun. We compare the average star forming DOG to the average bright (S850>5 mJy) submillimeter galaxy (SMG); the S24>100 microJy DOGs are 3 times more numerous but 8 times less luminous in the IR. The far-IR SED shape of DOGs is similar to that of SMGs (average dust temperature of around 30 K) but DOGs have a higher mid-IR to far-IR flux ratio. The average star formation-dominated DOG has a star formation rate of 200 Msun/yr which, given their space density, amounts to a contribution of 0.01 Msun/yr/Mpc3 (or 5-10%) to the star formation rate density at z~2. We use the composite SED to predict the average flux of DOGs in future Herschel/PACS 100 micron and SCUBA-2 450 micron surveys and show that the majority of them will be detected.
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.
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