4 research outputs found
A Pair of Compact Red Galaxies at Redshift 2.38, Immersed in a 100 kpc Scale Ly-alpha Nebula
We present Hubble Space Telescope (HST) and ground-based observations of a
pair of galaxies at redshift 2.38, which are collectively known as 2142-4420 B1
(Francis et al. 1996). The two galaxies are both luminous extremely red objects
(EROs), separated by 0.8 arcsec. They are embedded within a 100 kpc scale
diffuse Ly-alpha nebula (or blob) of luminosity ~10^44 erg/s.
The radial profiles and colors of both red objects are most naturally
explained if they are young elliptical galaxies: the most distant yet found. It
is not, however, possible to rule out a model in which they are abnormally
compact, extremely dusty starbursting disk galaxies. If they are elliptical
galaxies, their stellar populations have inferred masses of ~10^11 solar masses
and ages of ~7x10^8 years. Both galaxies have color gradients: their centers
are significantly bluer than their outer regions. The surface brightness of
both galaxies is roughly an order of magnitude greater than would be predicted
by the Kormendy relation. A chain of diffuse star formation extending 1 arcsec
from the galaxies may be evidence that they are interacting or merging.
The Ly-alpha nebula surrounding the galaxies shows apparent velocity
substructure of amplitude ~ 700 km/s. We propose that the Ly-alpha emission
from this nebula may be produced by fast shocks, powered either by a galactic
superwind or by the release of gravitational potential energy.Comment: 33 pages, 9 figures, ApJ in press (to appear in Jun 10 issue
Hubble Space Telescope STIS Observations of GRB 000301C: CCD Imaging and Near-Ultraviolet MAMA Spectroscopy
We present Space Telescope Imaging Spectrograph observations of the optical transient (OT) counterpart of the γ-ray burster GRB 000301C obtained 5 days after the burst, on 2000 March 6. CCD clear-aperture imaging reveals a R ≃ 21.50 ± 0.15 source with no apparent host galaxy. An 8000 s, 1150 Å 18 on the line of sight to the OT. This measured redshift is conservatively a lower limit to the GRB redshift. However, as all other GRBs that have deep Hubble Space Telescope images appear to lie on the stellar field of a host galaxy, and as the large H I column density measured here and in later ground-based observations is unlikely on a random line of sight, we believe we are probably seeing absorption from H I in the host galaxy. In any case, this represents the largest direct redshift determination of a γ-ray burster to date. Our data are compatible with an OT spectrum represented by a power law with an intrinsic index α = 1.2 (f_ν ∝ ν^(-α)) and no extinction in the host galaxy, or with α = 0.5 and extinction by SMC-like dust in the OT rest frame with A_V = 0.15. The large N_(H I) and the lack of a detected host are similar to the situation for damped Lyα absorbers at z > 2
HST/STIS observations of GRB000301C: CCD imaging and NUV MAMA spectroscopy
We present HST/STIS observations of the optical counterpart (OT) of the
gamma-ray burster GRB 000301C obtained on 2000 March 6, five days after the
burst. CCD clear aperture imaging reveals a R ~ 21.50+/-0.15 source with no
apparent host galaxy. An 8000 s, 1150 < lambda/A < 3300 NUV-MAMA prism spectrum
shows a relatively flat continuum (in f_lambda) between 2800 and 3300 A, with a
mean flux 8.7 (+0.8,-1.6)+/- 2.6 10^(-18) ergs/s/cm^2/A, and a sharp break
centered at 2797+/-25 A. We interpret it as HI Lyman break at z = 2.067+/-0.025
indicating the presence of a cloud with a HI column density log(HI) > 18 on the
line-of-sight to the OT. This value is conservatively a lower limit to the GRB
redshift. However, the facts that large N(HI) system are usually considered as
progenitors of present day galaxies and that other OTs are found associated
with star forming galaxies strongly suggest that it is the GRB redshift. In any
case, this represents the largest direct redshift determination of a gamma-ray
burster to date. Our data are compatible with an OT spectrum represented by a
power-law with an intrinsic index \alpha = 1.2((f_nu \propto nu^-alpha) and no
extinction in the host galaxy or with alpha = 0.5 and extinction by a SMC-like
dust in the OT rest-frame with A_V = 0.15. The large N(HI) and the lack of
detected host is similar to the situation for damped Ly-alpha absorbers at z >
2.Comment: Replaced by final version. 10 p., 2 fig. Scheduled to appear in ApJ
555 n2 Jul 10, 2001. Minor changes, both redshift and mean near UV flux are
revised with slightly larger values, due to a wrong offset sign in the
wavelength calibratio
Hubble Space Telescope STIS Observations of GRB 000301C: CCD Imaging and Near-Ultraviolet MAMA Spectroscopy
We present Space Telescope Imaging Spectrograph observations of the optical transient (OT) counterpart of the γ-ray burster GRB 000301C obtained 5 days after the burst, on 2000 March 6. CCD clear-aperture imaging reveals a R ≃ 21.50 ± 0.15 source with no apparent host galaxy. An 8000 s, 1150 Å 18 on the line of sight to the OT. This measured redshift is conservatively a lower limit to the GRB redshift. However, as all other GRBs that have deep Hubble Space Telescope images appear to lie on the stellar field of a host galaxy, and as the large H I column density measured here and in later ground-based observations is unlikely on a random line of sight, we believe we are probably seeing absorption from H I in the host galaxy. In any case, this represents the largest direct redshift determination of a γ-ray burster to date. Our data are compatible with an OT spectrum represented by a power law with an intrinsic index α = 1.2 (f_ν ∝ ν^(-α)) and no extinction in the host galaxy, or with α = 0.5 and extinction by SMC-like dust in the OT rest frame with A_V = 0.15. The large N_(H I) and the lack of a detected host are similar to the situation for damped Lyα absorbers at z > 2