475 research outputs found
Dust production 680-850 million years after the Big Bang
Dust plays an important role in our understanding of the Universe, but it is
not obvious yet how the dust in the distant universe was formed. I derived the
dust yields per asymptotic giant branch (AGB) star and per supernova (SN)
required to explain dust masses of galaxies at z=6.3-7.5 (680-850 million years
after the Big Bang) for which dust emission has been detected (HFLS3 at z=6.34,
ULAS J1120+0641 at z=7.085, and A1689-zD1 at z=7.5), or unsuccessfully searched
for. I found very high required yields, implying that AGB stars could not
contribute substantially to dust production at these redshifts, and that SNe
could explain these dust masses, but only if they do not destroy most of the
dust they form (which is unlikely given the upper limits on the SN dust yields
derived for galaxies where dust is not detected). This suggests that the grain
growth in the interstellar medium is likely required at these early epochs.Comment: Accepted to A&A. 6 pages, 1 figure, 2 tables. V2: minor changes to
match the published versio
Spectral energy distributions of submm/radio bright gamma-ray burst host galaxies
We present optical to radio spectral energy distribution fitting of the host
galaxies of four long gamma-ray bursts: 980703, 000210, 000418 and 010222,
which were detected at submillimetre and/or radio wavelengths. We find that
only very young starburst galaxy models are consistent with the data having
both blue optical colors and a pronounced submm emission. For each host we are
able to construct a model consistent with the short- and long-wavelength parts
of the spectra. We find galaxy ages ranging from 0.09 to 2.0 Gyrs and star
formation rates ranging from 138 to 380 MSun/yr.Comment: 6 pages, 1 figure, Proceedings of the Conference "The Multicoloured
Landscape of Compact Objects and their Explosive Origins" (Cefalu, Sicily,
2006 June 11-24). Eds. L. Burderi et al. (New York: AIP), in press, for SED
templates, see http://archive.dark-cosmology.dk
Dust production scenarios in galaxies at z ~ 6-8.3
The mechanism of dust formation in galaxies at high redshift is still
unknown. Asymptotic giant branch (AGB) stars and explosions of supernovae (SNe)
are possible dust producers, and non-stellar processes may substantially
contribute to dust production, for example grain growth in the interstellar
medium (ISM). Our aim is to determine the contribution to dust production of
AGB stars and SNe in nine galaxies at z ~ 6-8.3, for which observations of dust
have been recently attempted. In order to determine the origin of the observed
dust we have determined dust yields per AGB star and SN required to explain the
total amounts of dust in these galaxies. We find that AGB stars were not able
to produce the amounts of dust observed in the galaxies in our sample. In order
to explain these dust masses, SNe would have to have maximum efficiency and not
destroy the dust which they formed. Therefore, the observed amounts of dust in
the galaxies in the early universe were formed either by efficient supernovae
or by a non-stellar mechanism, for instance the grain growth in the
interstellar medium.Comment: Accepted for publication in A&A, 5 pages, 1 figur
Shaping the dust mass - star-formation rate relation
There is a remarkably tight relation between the observationally inferred
dust masses and star-formation rates (SFRs) of SDSS galaxies, Mdust
SFR (Da Cunha et al. 2010). Here we extend the Mdust-SFR relation to
the high end and show that it bends over at very large SFRs (i.e., dust masses
are lower than predicted for a given SFR). We identify several distinct
evolutionary processes in the diagram: (1) A star-bursting phase in which dust
builds up rapidly at early times. The maximum attainable dust mass in this
process is the cause of the bend-over of the relation. A high dust-formation
efficiency, a bottom-light initial mass function, and negligible supernova
shock dust destruction are required to produce sufficiently high dust masses.
(2) A quiescent star-forming phase in which the subsequent parallel decline in
dust mass and SFR gives rise to the Mdust-SFR relation, through astration and
dust destruction. The dust-to-gas ratio is approximately constant along the
relation. We show that the power-law slope of the Mdust-SFR relation is
inversely proportional to the global Schmidt-Kennicutt law exponent (i.e.,
) in simple chemical evolution models. (3) A quenching phase which
causes star formation to drop while the dust mass stays roughly constant or
drops proportionally. Combined with merging, these processes, as well as the
range in total baryonic mass, give rise to a complex population of the diagram
which adds significant scatter to the original Mdust-SFR relation. (4) At very
high redshifts, a population of galaxies located significantly below the local
relation is predicted.Comment: 5 pages, 1 figure, ApJL, in pres
First measurement of HI 21cm emission from a GRB host galaxy indicates a post-merger system
We report the detection and mapping of atomic hydrogen in HI 21cm emission
from ESO 184-G82, the host galaxy of the gamma ray burst 980425. This is the
first instance where HI in emission has been detected from a galaxy hosting a
gamma ray burst. ESO 184-G82 is an isolated galaxy and contains a Wolf-Rayet
region close to the location of the gamma ray burst and the associated
supernova, SN 1998bw. This is one of the most luminous HII regions identified
in the local Universe, with a very high inferred density of star formation. The
HI 21cm observations reveal a high HI mass for the galaxy, twice as large as
the stellar mass. The spatial and velocity distribution of the HI 21cm emission
reveals a disturbed rotating gas disk, which suggests that the galaxy has
undergone a recent minor merger that disrupted its rotation. We find that the
Wolf-Rayet region and the gamma ray burst are both located in the highest HI
column density region of the galaxy. We speculate that the merger event has
resulted in shock compression of the gas, triggering extreme star formation
activity, and resulting in the formation of both the Wolf-Rayet region and the
gamma ray burst. The high HI column density environment of the GRB is
consistent with the high HI column densities seen in absorption in the host
galaxies of high redshift gamma ray bursts.Comment: Accepted for publication in MNRAS Letters. 5 pages, 5 figures, 2
tables. For the definitive version visit http://mnrasl.oxfordjournals.org
On the Distribution of Stellar Masses in Gamma-ray Burst Host Galaxies
We analyze Spitzer images of 30 long-duration gamma-ray burst (GRB) host galaxies. We estimate their total stellar masses (M_*) based on the rest-frame K-band luminosities (L_K_(rest)) and constrain their star formation rates (SFRs; not corrected for dust extinction) based on the rest-frame UV continua. Further, we compute a mean M_*/ L_K_(rest) = 0.45 M_☉/L_☉. We find that the hosts are low M_*, star-forming systems. The median M_* in our sample ( = 10^(9.7) M_☉) is lower than that of "field" galaxies (e.g., Gemini Deep Deep Survey). The range spanned by M_* is 10^7 M_☉ < M_* < 10^(11) M_☉, while the range spanned by the dust-uncorrected UV SFR is 10^(–2) M_☉ yr^(–1) < SFR < 10 M_☉ yr^(–1). There is no evidence for intrinsic evolution in the distribution of M_* with redshift. We show that extinction by dust must be present in at least 25% of the GRB hosts in our sample and suggest that this is a way to reconcile our finding of a relatively lower UV-based, specific SFR (φ ≡ SFR/M_*) with previous claims that GRBs have some of the highest φ values. We also examine the effect that the inability to resolve the star-forming regions in the hosts has on φ
Dust grain growth in the interstellar medium of 5<z<6.5 quasars
We investigate whether stellar dust sources i.e. asymptotic giant branch
(AGB) stars and supernovae (SNe) can account for dust detected in 5<z<6.5
quasars (QSOs). We calculate the required dust yields per AGB star and per SN
using the dust masses of QSOs inferred from their millimeter emission and
stellar masses approximated as the difference between the dynamical and the H_2
gas masses of these objects. We find that AGB stars are not efficient enough to
form dust in the majority of the z>5 QSOs, whereas SNe may be able to account
for dust in some QSOs. However, they require very high dust yields even for a
top-heavy initial mass function. This suggests additional non-stellar dust
formation mechanism e.g. significant dust grain growth in the interstellar
medium of at least three out of nine z>5 QSOs. SNe (but not AGB stars) may
deliver enough heavy elements to fuel this growth.Comment: A&A, accepted. 5 pages, 2 figures, 2 table
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