959 research outputs found
Measures of galaxy dust and gas mass with Herschel photometry and prospects for ALMA
(Abridged) Combining the deepest Herschel extragalactic surveys (PEP,
GOODS-H, HerMES), and Monte Carlo mock catalogs, we explore the robustness of
dust mass estimates based on modeling of broad band spectral energy
distributions (SEDs) with two popular approaches: Draine & Li (2007, DL07) and
a modified black body (MBB). As long as the observed SED extends to at least
160-200 micron in the rest frame, M(dust) can be recovered with a >3 sigma
significance and without the occurrence of systematics. An average offset of a
factor ~1.5 exists between DL07- and MBB-based dust masses, based on consistent
dust properties. At the depth of the deepest Herschel surveys (in the GOODS-S
field) it is possible to retrieve dust masses with a S/N>=3 for galaxies on the
main sequence of star formation (MS) down to M(stars)~1e10 [M(sun)] up to z~1.
At higher redshift (z<=2) the same result is achieved only for objects at the
tip of the MS or lying above it. Molecular gas masses, obtained converting
M(dust) through the metallicity-dependent gas-to-dust ratio delta(GDR), are
consistent with those based on the scaling of depletion time, and on CO
spectroscopy. Focusing on CO-detected galaxies at z>1, the delta(GDR)
dependence on metallicity is consistent with the local relation. We combine
far-IR Herschel data and sub-mm ALMA expected fluxes to study the advantages of
a full SED coverage.Comment: Accepted for publication in Astronomy and Astrophysics. Some figures
have degraded quality for filesize reason
Nuclear Dynamics and Star Formation of AGN
We are using adaptive optics on Keck and the VLT to probe the dynamics and
star formation in Seyfert and QSO nuclei, obtaining spatial resolutions better
than 0.1" in the H- and K-bands. The dynamics are traced via the 2.12um H_2
1-0S(1) line, while the stellar cluster is traced through the CO 2-0 and 6-3
absorption bandheads at 2.29um and 1.62um respectively. Matching disk models to
the H_2 rotation curves allows us to study nuclear rings, bars, and warps; and
to constrain the mass of the central black hole. The spatial extent and
equivalent width of the stellar absorption permits us to estimate the mass of
stars in the nucleus and their contribution to the emission. Here we report on
new data for I Zwicky 1, Markarian 231, and NGC 7469.Comment: 6 page contribution to 'Science with Adaptive Optics
ALFA & 3D: integral field spectroscopy with adaptive optics
One of the most important techniques for astrophysics with adaptive optics is
the ability to do spectroscopy at diffraction limited scales. The extreme
difficulty of positioning a faint target accurately on a very narrow slit can
be avoided by using an integral field unit, which provides the added benefit of
full spatial coverage. During 1998, working with ALFA and the 3D integral field
spectrometer, we demonstrated the validity of this technique by extracting and
distinguishing spectra from binary stars separated by only 0.26". The
combination of ALFA & 3D is also ideally suited to imaging distant galaxies or
the nuclei of nearby ones, as its field of view can be changed between
1.2"x1.2" and 4"x4", depending on the pixel scale chosen. In this contribution
we present new results both on galactic targets, namely young stellar objects,
as well as extra-galactic objects including a Seyfert and a starburst nucleus.Comment: SPIE meeting 4007 on Adaptive Optical Systems Technology, March 200
Stellar Dynamics and the implications on the merger evolution in NGC6240
We report near-infrared integral field spectroscopy of the luminous merging
galaxy NGC 6240. Stellar velocities show that the two K-band peaks separated by
1.6arcsec are the central parts of inclined, rotating disk galaxies with equal
mass bulges. The dynamical masses of the nuclei are much larger than the
stellar mass derived from the K-band light, implying that the progenitor
galaxies were galaxies with massive bulges. The K-band light is dominated by
red supergiants formed in the two nuclei in starbursts, triggered ~2x10^7 years
ago, possibly by the most recent perigalactic approach. Strong feedback effects
of a superwind and supernovae are responsible for a short duration burst
(~5x10^6 years) which is already decaying. The two galaxies form a
prograde-retrograde rotating system and from the stellar velocity field it
seems that one of the two interacting galaxies is subject to a prograde
encounter. Between the stellar nuclei is a prominent peak of molecular gas
(H_2, CO). The stellar velocity dispersion peaks there indicating that the gas
has formed a local, self-gravitating concentration decoupled from the stellar
gravitational potential. NGC 6240 has previously been reported to fit the
paradigm of an elliptical galaxy formed through the merger of two galaxies.
This was based on the near-infrared light distribution which follows a
r^1/4-law. Our data cast strong doubt on this conclusion: the system is by far
not relaxed, rotation plays an important role, as does self-gravitating gas,
and the near-infrared light is dominated by young stars.Comment: 34 pages, 11 figures, using AASTEX 5.0rc3.1, paper submitted to the
Astrophysical Journal, revised versio
Counterrotating Nuclear Disks in Arp 220
The ultraluminous infrared galaxy Arp 220 has been observed at 0.5"
resolution in CO(2-1) and 1 mm continuum using the newly expanded Owens Valley
Millimeter Array. The CO and continuum peaks at the double nuclei and the
surrounding molecular gas disk are clearly resolved. We find steep velocity
gradients across each nucleus (dV ~ 500 km/s within r= 0.3") whose directions
are not aligned with each other and with that of the outer gas disk. We
conclude that the double nuclei have their own gas disks (r ~ 100 pc). They are
counterrotating with respect to each other and embedded in the outer gas disk
(r ~ 1 kpc) rotating around the dynamical center of the system. The masses of
each nucleus are M_dyn > 2* 10^9 M_sun based on the CO kinematics. Although
there is no evidence of an old stellar population in the optical or near
infrared spectroscopy of the nuclei (probably due to the much brighter young
population), it seems likely that these nuclei were 'seeded' from the
pre-merger nuclei in view of their counterrotating gas kinematics. The gas
disks probably constitute a significant fraction (~ 50 %) of the mass in each
nucleus. The CO and continuum brightness temperatures imply that the nuclear
gas disks have high area filling factors (~ 0.5-1) and have extremely high
visual extinctions (Av ~ 1000 mag). The molecular gas must be hot (>= 40 K) and
dense (>= 10^4-5 cm^-3), given the large mass and small scale-height of the
nuclear disks. The continuum data suggest that the large luminosity (be it
starburst or AGN) must originate within 100 pc of the two nuclear gas disks
which were presumably formed through concentration of gas from the progenitor
outer galaxy disks.Comment: 20 pages, 5 figures. Accepted for publication in The Astrophysical
Journa
Intense Star-formation and Feedback at High Redshift: Spatially-resolved Properties of the z=2.6 Submillimeter Galaxy SMMJ14011+0252
We present a detailed analysis of the spatially-resolved properties of the
lensed submillimeter galaxy SMMJ14011+0252 at z=2.56, combining deep
near-infrared integral-field data obtained with SPIFFI on the VLT with other
multi-wavelength data sets. The broad characteristics of SMMJ14011+0252 are in
agreement with what is expected for the early evolution of local massive
spheroidal galaxies. From continuum and line flux, velocity, and dispersion
maps, we measure the kinematics, star-formation rates, gas densities, and
extinction for individual subcomponents. The star formation intensity is
similar to low-redshift ``maximal starbursts'', while the line fluxes and the
dynamics of the emission line gas provide direct evidence for a
starburst-driven wind with physical properties very similar to local
superwinds. We also find circumstantial evidence for "self-regulated" star
formation within J1. The relative velocity of the bluer companion J2 yields a
dynamical mass estimate for J1 within about 20 kpc, M_dyn \sim 1\times 10^{11}
M_sun. The relative metallicity of J2 is 0.4 dex lower than in J1n/s,
suggesting different star formation histories. SED fitting of the continuum
peak J1c confirms and substantiates previous suggestions that this component is
a z=0.25 interloper. When removing J1c, the stellar continuum and H-alpha line
emission appear well aligned spatially in two individual components J1n and
J1s, and coincide with two kinematically distinct regions in the velocity map,
which might well indicate a merging system. This highlights the close
similarity between SMGs and ULIRGs, which are often merger-driven maximal
starbursts, and suggests that the intrinsic mechanisms of star-formation and
related feedback are similar to low-redshift strongly star-forming systems.Comment: Some of the figures changed from b/w to colo
SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution
We present 0.5" resolution near-IR integral field spectroscopy of the Ha line
emission of 14 z~2 UV-selected BM/BX galaxies obtained with SINFONI at ESO/VLT.
The mean Ha half-light radius r_1/2 is about 4kpc and line emission is detected
over > ~20kpc in several sources. In 9 sources, we detect spatially-resolved
velocity gradients, from 40 to 410 km/s over ~10kpc. The observed kinematics of
the larger systems are consistent with orbital motions. Four galaxies are well
described by rotating disks with clumpy morphologies and we extract rotation
curves out to radii > ~10kpc. One or two galaxies exhibit signatures more
consistent with mergers. Analyzing all 14 galaxies in the framework of rotating
disks, we infer mean inclination- and beam-corrected maximum circular
velocities v_c of 180+-90 km/s and dynamical masses of (0.5-25)x10^10 Msun
within r_1/2. On average, the dynamical masses are consistent with photometric
stellar masses assuming a Chabrier/Kroupa IMF but too small for a 0.1-100 Msun
Salpeter IMF. The specific angular momenta of our BM/BX galaxies are similar to
those of local late-type galaxies. The specific angular momenta of their
baryons are comparable to those of their dark matter halos. Extrapolating from
the average v_c at 10kpc, the virial mass of the typical halo of a galaxy in
our sample is 10^(11.7+-0.5) Msun. Kinematic modeling of the 3 best cases
implies a ratio of v_c to local velocity dispersion of order 2-4 and
accordingly a large geometric thickness. We argue that this suggests a mass
accretion (alternatively, gas exhaustion) timescale of ~500Myr. We also argue
that if our BM/BX galaxies were initially gas rich, their clumpy disks will
subsequently lose their angular momentum and form compact bulges on a timescale
of ~1 Gyr. [ABRIDGED]Comment: Accepted for publication in the Astrophysical Journal. 17 pages, 5
color figure
Constraint on the Assembly and Dynamics of Galaxies. II. Properties of Kiloparsec-Scale Clumps in Rest-Frame Optical Emission of z ~ 2 Star-Forming Galaxies
We study the properties of luminous stellar "clumps" identified in deep, high-resolution Hubble Space Telescope NIC2/F160W imaging at 1.6 μm of six z ~ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. Individual clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ≈5000 Å emission, with median of ≈2%; the total contribution of clump light ranges from 10% to 25%. The median intrinsic clump size and stellar mass are ~1 kpc and ~10^9 M_☉, in the ranges for clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation through gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with Advanced Camera for Surveys (ACS)/F814W imaging available for one source, and adaptive-optics-assisted SINFONI Hα data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of clumps identified at different wavelengths do not fully overlap; NIC2-identified clumps tend to be redder/older than ACS- or Hα-identified clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the clumps, consistent with scenarios where inward migration of clumps transports material toward the central regions. From constraints on a bulge-like component at radii ≾1-3 kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the buildup of stellar bulges and the role of clumps in this process
Lyman Break Galaxies Under a Microscope: The Small Scale Dynamics and Mass of an Arc in the Cluster 1E0657-56
Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we
have studied the spatially-resolved dynamics in the z=3.2 strongly lensed
galaxy 1E0657-56 ``arc+core''. The lensing configuration suggests that the high
surface brightness ``core'' is the M=20 magnified central 1 kpc of the galaxy
(seen at a spatial resolution of about 200 pc in the source plane), whereas the
fainter ``arc'' is a more strongly magnified peripheral region of the same
galaxy at about a half-light radius, which otherwise appears to be a typical
z=3 Lyman break galaxy.
The overall shape of the position-velocity diagram resembles the ``rotation
curves'' of the inner few kpcs of nearby L* spiral galaxies. The projected
velocities rise rapidly to 75 km/s within the core. This implies a dynamical
mass of M_dyn = 10^9.3 M_sun within the central kpc, and suggests that in this
system the equivalent of the mass of a present-day L* bulge at the same radius
was already in place by z>=3. Approximating the circular velocity of the halo
by the measured asymptotic velocity of the rotation curve, we estimate a dark
matter halo mass of M_halo = 10^11.7 +/- 0.3, in good agreement with
large-scale clustering studies of Lyman break galaxies. The baryonic collapse
fraction is low compared to actively star-forming ``BX'' and low-redshift
galaxies around z=2, perhaps implying comparatively less gas infall to small
radii or efficient feedback. Even more speculatively, the high central mass
density might indicate highly dissipative gas collapse in very early stages of
galaxy evolution, in approximate agreement with what is expected for
``inside-out'' galaxy formation models.Comment: Accepted for publication in the Astrophysical Journa
The Far-Infrared, UV and Molecular Gas Relation in Galaxies up to z=2.5
We use the infrared excess (IRX) FIR/UV luminosity ratio to study the
relation between the effective UV attenuation (A_IRX) and the UV spectral slope
(beta) in a sample of 450 1<z<2.5 galaxies. The FIR data is from very deep
Herschel observations in the GOODS fields that allow us to detect galaxies with
SFRs typical of galaxies with log(M)>9.3. Thus, we are able to study galaxies
on and even below the main SFR-stellar mass relation (main sequence). We find
that main sequence galaxies form a tight sequence in the IRX--beta plane, which
has a flatter slope than commonly used relations. This slope favors a SMC-like
UV extinction curve, though the interpretation is model dependent. The scatter
in the IRX-beta plane, correlates with the position of the galaxies in the
SFR-M plane. Using a smaller sample of galaxies with CO gas masses, we study
the relation between the UV attenuation and the molecular gas content. We find
a very tight relation between the scatter in the IRX-beta plane and the
specific attenuation (S_A), a quantity that represents the attenuation
contributed by the molecular gas mass per young star. S_A is sensitive to both
the geometrical arrangement of stars and dust, and to the compactness of the
star forming regions. We use this empirical relation to derive a method for
estimating molecular gas masses using only widely available integrated
rest-frame UV and FIR photometry. The method produces gas masses with an
accuracy between 0.12-0.16 dex in samples of normal galaxies between z~0 and
z~1.5. Major mergers and sub-millimeter galaxies follow a different S_A
relation.Comment: 11 pages, 6 pages appendix, 11 figures, accepted to Ap
- …