231 research outputs found
Spatially Resolved Near-Infrared Spectroscopy of Seyfert 2 Galaxies Mk 1066, NGC 2110, NGC 4388, and Mk 3
We present near-infrared spectra with resolutions of lambda/dlambda~1200 in
the emission lines of Pa-beta, [FeII] (1.2567um), Br-gamma, and H2 v=1-0S(1) of
the nuclei and circumnuclear regions of the four Seyfert 2 galaxies Mk 1066,
NGC 2110, NGC 4388, and Mk 3. All of these galaxies show strong near-infrared
line emission that is detected at radii several times the spatial resolution,
corresponding to projected physical scales of 0.07 to 0.7 kpc. Velocity
gradients are detected in these nuclei, as are spatial variations in line
profiles and flux ratios. We compare the spatial and velocity distribution of
the line emission to previously observed optical line and radio emission. The
evidence indicates that the [FeII] emission is associated with the Seyfert
activity in the galaxies. Our data are consistent with X-ray heating being
responsible for most of the [FeII] emission, although differences in [FeII] and
Pa-beta line profiles associated with radio emission suggests that the [FeII]
emission is enhanced by fast shocks associated with radio outflows. The H2
emission is not as strongly associated with outflows or ionization cones as is
the emission in other lines, but rather appears to be primarily associated with
the disk of the galaxy.Comment: 35 pages, 24 figure
Gas and Dust Emission from the Nuclear Region of the Circinus Galaxy
Simultaneous modeling of the line and continuum emission from the nuclear
region of the Circinus galaxy is presented. Composite models which include the
combined effect of shocks and photoionization from the active center and from
the circumnuclear star forming region are considered. The effects of dust
reradiation, bremsstrahlung from the gas and synchrotron radiation are treated
consistently. The proposed model accounts for two important observational
features. First, the high obscuration of Circinus central source is produced by
high velocity and dense clouds with characteristic high dust-to-gas ratios.
Their large velocities, up to 1500 km\s, place them very close to the active
center. Second, the derived size of the line emitting region is well in
agreement with the observed limits for the coronal and narrow line region of
Circinus.Comment: 36 pages, LaTex (including 4 Tables and 9 figures), removed from
Abstract To appear in "The Astrophysical Journal
Faint InfraRed Extragalactic Survey: Data and Source Catalogue of the MS1054-03 field
We present deep near-infrared Js, H, and Ks band imaging of a field around
MS1054-03, a massive cluster at z=0.83. The observations were carried out with
ISAAC at the ESO VLT as part of the Faint InfraRed Extragalactic Survey
(FIRES). The total integration time amounts to 25.9h in Js, 24.4h in H, and
26.5h in Ks, divided nearly equally between four pointings covering 5.5'x5.3'.
The 3-sigma total limiting AB magnitudes for point sources from the shallowest
to deepest pointing are Js=26.0-26.2, H=25.5-25.8, and Ks=25.3-25.7. The
effective spatial resolution of the coadded images has FWHM=0.48", 0.46", and
0.52" in Js, H, and Ks. We complemented the ISAAC data with deep optical
imaging using existing HST WFPC2 mosaics in the F606W and F814W filters and new
U, B and V band data from VLT FORS1. We constructed a Ks-band limited
multicolour source catalogue to Ks(total,AB)=25 (about 5-sigma for point
sources). The catalogue contains 1858 objects, of which 1663 have eight-band
photometry. We describe the observations, data reduction, source detection and
photometric measurements method. We present the number counts, colour
distributions, and photometric redshifts z_ph of the catalogue sources. We find
that our counts at the faint end 22<Ks(AB)<25, with slope dlog(N)/dm=0.20, lie
at the flatter end of published counts in other deep fields and are consistent
with those we derived in the HDF-South, the other FIRES field. Spectroscopic
redshifts z_sp are available for about 330 sources in the MS1054-03 field;
comparison between the z_ph and z_sp shows very good agreement, with
=0.078. The MS1054-03 field observations complement our
HDF-South data set with nearly five times larger area at about 0.7 brighter
magnitudes. [ABRIDGED]Comment: Accepted for publication in the Astronomical Journal. 32 pages, 14
b/w figures, 1 color figur
Kinematics of Galaxies in the Hubble Deep Field South: Discovery of a Very Massive Spiral at z=0.6
We report the first results from a study of the internal kinematics, based on
spatially resolved H_alpha velocity profiles, of three galaxies at redshift
z~0.6 and one at redshift z~0.8, detected by ISOCAM in the Hubble Deep Field
South. The kinematics are derived from high resolution near-infrared VLT
spectroscopy. One of the galaxies is a massive spiral which possesses a very
large rotational velocity of 460 km/s and contains a mass of 10^12 M_solar
(within 20 kpc), significantly higher than the dynamical masses measured in
most other local and high redshift spirals. Two of the galaxies comprise a
counter-rotating interacting system, while the fourth is also a large spiral.
The observed galaxies are representative examples of the morphologies
encountered among ISOCAM galaxies. The mass-to-light (M /L_bol) ratios of
ISOCAM galaxies lie between those of local luminous IR galaxies and massive
spirals. We measure an offset of 1.6+/-0.3 mag in the rest frame B-band and of
0.7+/-0.3 mag in the rest frame I-band when we compare the four ISOCAM galaxies
to the local Tully-Fisher B and I-band relations. We conclude that the large IR
luminosity of the ISOCAM population results from a combination of large mass
and efficient triggering of star formation. Since ISOCAM galaxies contribute
significantly to the Cosmic Infrared Background our results imply that a
relatively small number of very massive and IR luminous objects contribute
significantly to the IR background and star formation activity near z~0.7.Comment: accepted for publication in the Astrophysical Journal (Part 1
The lack of intense Lyman~alpha in ultradeep spectra of z=7 candidates in GOODS-S: imprint of reionization?
We present ultradeep optical spectroscopy obtained with FORS2 on VLT of seven
Lyman-break galaxy (LBG) candidates at z>6.5 selected in the GOODS-S field from
Hawk-I/VLT and WFC3/HST imaging. For one galaxy we detect a low significance
emission line (S/N< 7), located at 9691.5 +/- 0.5A and with flux 3.4 x
10^(-18)erg/cm^2/s. If identified as Lyman alpha, it places the LBG at redshift
z=6.972+/- 0.002, with a rest-frame equivalent width EW}=13A. Using Monte Carlo
simulations and conservative EW distribution functions at 2<z<6, we estimate
that the probability of observing no galaxies in our data with S/N>10 is ~ 2%,
and that of observing only one galaxy out of seven with S/N=5 is ~4%, but these
can be as small as ~1E-3, depending on the details of the EW distribution. We
conclude that either a significant fraction of the candidates is not at high
redshift or that some physical mechanism quenches the Lyman alpha emission
emerging from the galaxies at z>6.5, abruptly reversing the trend of the
increasing fraction of strong emitters with increasing redshift observed up to
z~ 6.5. We discuss the possibility that an increasingly neutral intergalactic
medium is responsible for such quenching.Comment: Submitted to ApJL: re-submitted version after modification responding
to the referee's repor
Search for clusters at high redshift - I. Candidate Lya emitters near 1138-262 at z=2.2
Radio, optical and X-ray observations of the powerful radio galaxy PKS
1138-262 at z=2.156 have suggested that this galaxy is a massive galaxy in the
center of a forming cluster. We have imaged 1138-262 and the surrounding 38
square arcminute field with the Very Large Telescope in a broad band and a
narrow band encompassing the redshifted Lya emission. We detect 50 objects with
rest equivalent width larger than 20 A and a luminous, highly extended Lya halo
around 1138-262. If the radio galaxy is at the center of a forming cluster,
these objects are candidate Lya emitting cluster galaxies.Comment: Accepted for publication in A&A as Letter, 4 pages, 4 figure
Circumnuclear obscuration of the Circinus galaxy by a starburst-radiation supported wall
We consider the radiation-hydrodynamical formation of a dusty wall in the
circumnuclear regions of the Circinus Seyfert 2 galaxy. We focus on the
radiative flux force due to the circumnuclear starburst, the nuclear starburst
and the active galactic nucleus (AGN), and analyze the equilibrium
configuration and stability of the dusty gas in the circumnuclear regions. The
mass distributions used to model the gravitational fields are determined by the
observed rotation velocities of the stars and of the gas. Moreover, by using
the simple stellar evolution in the circumnuclear starburst, the bolometric
luminosity of the starburst is estimated as a function of time. As a result, it
is shown that the radiation force by the circumnuclear starburst does play an
important role to build up a radiatively-supported dusty wall of \la 100 pc,
which obscures the circumnuclear regions with of a few magnitudes. It is
also found that the age of a circumnuclear starburst when the circumnuclear
regions are enshrouded by the dusty wall is constrained to be \la 10^8 yr,
which is consistent with the age observationally inferred for the starburst, yr yr.Comment: 6 pages, 4 figures, accepted for publication in A&
H-alpha Spectroscopy of Galaxies at z>2: Kinematics and Star Formation
We present near-infrared spectroscopy of H-alpha emission lines in a sample
of 16 star-forming galaxies at redshifts 2.0<z<2.6. Our targets are drawn from
a large sample of galaxies photometrically selected and spectroscopically
confirmed to lie in this redshift range. Six of the galaxies exhibit spatially
extended, tilted H-alpha emission lines; rotation curves for these objects
reach mean velocities of ~150 km/s at radii of ~6 kpc, without corrections for
any observational effects. The velocities and radii give a mean dynamical mass
of M>4e10 M_sun. One-dimensional velocity dispersions for the 16 galaxies range
from ~50 to ~260 km/s, and in cases where we have both virial masses implied by
the velocity dispersions and dynamical masses derived from the spatially
extended emission lines, they are in rough agreement. We compare our kinematic
results to similar measurements made at z~3, and find that both the observed
rotational velocities and velocity dispersions tend to be larger at z~2 than at
z~3. We find a mean SFR_H-alpha of 16 M_sun/yr and an average
SFR_H-alpha/SFR_UV ratio of 2.4, without correcting for extinction. We see
moderate evidence for an inverse correlation between the UV continuum
luminosity and the ratio SFR_H-alpha/SFR_UV, such as might be observed if the
UV-faint galaxies suffered greater extinction. We discuss the effects of dust
and star formation history on the SFRs, and conclude that extinction is the
most likely explanation for the discrepancy between the two SFRs.Comment: 20 pages, 9 figures. Accepted by Ap
Spectroscopic confirmation of two Lyman break galaxies at redshift beyond 7
We report the spectroscopic confirmation of two Lyman break galaxies at
redshift > 7. The galaxies were observed as part of an ultra-deep spectroscopic
campaign with FORS2 at the ESO/VLT for the confirmation of z~7 ``z--band
dropout'' candidates selected from our VLT/Hawk-I imaging survey. Both galaxies
show a prominent emission line at 9735A and 9858A respectively: the lines have
fluxes of ~ 1.6-1.2 x 10^(-17) erg/s/cm2 and exhibit a sharp decline on the
blue side and a tail on the red side. The asymmetry is quantitatively
comparable to the observed asymmetry in z ~ 6 Ly-alpha lines, where absorption
by neutral hydrogen in the IGM truncates the blue side of the emission line
profile. We carefully evaluate the possibility that the galaxies are instead at
lower redshift and we are observing either [OII], [OIII] or H-alpha emission:
however from the spectroscopic and the photometric data we conclude that there
are no other plausible identifications, except for Ly-alpha at redshift >7,
implying that these are two of the most robust redshift determination for
galaxies in the reionization epoch. Based on their redshifts and broad--band
photometry, we derive limits on the star formation rate and on the ultraviolet
spectral slopes of the two galaxies. We argue that these two galaxies alone are
unlikely to have ionized the IGM in their surroundings.Comment: Accepted for publication in ApJL, 3 figures and one table, emulated
ap
Dynamical properties of Ultraluminous Infrared Galaxies I: Mass ratio conditions for ULIRG activity in interacting pairs
We present first results from our Very Large Telescope large program to study
the dynamical evolution of Ultraluminous Infrared Galaxies (ULIRGs), which are
the products of mergers of gas-rich galaxies. The full data set consists of
high resolution, long-slit, H- and K-band spectra of 38 ULIRGs and 12 QSOs
(between 0.042<z<0.268). In this paper, we present the sources that have not
fully coalesced, and therefore have two distinct nuclei. This sub-sample
consists of 21 ULIRGs, the nuclear separation of which varies between 1.6 and
23.3 kpc. From the CO bandheads that appear in our spectra, we extract the
stellar velocity dispersion, sigma, and the rotational velocity, V_rot. The
stellar dispersion equals 142 km/s on average, while V_rot is often of the same
order. We combine our spectroscopic results with high-resolution infrared (IR)
imaging data to study the conditions for ULIRG activity in interacting pairs.
We find that the majority of ULIRGs are triggered by almost equal-mass major
mergers of 1.5:1 average ratio. Less frequently, 3:1 encounters are also
observed in our sample. However, less violent mergers of mass ratio >3:1
typically do not force enough gas into the center to generate ULIRG
luminosities.Comment: Accepted for publication in "The Astrophysical Journal
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