1,346 research outputs found
The DiskMass Survey. X. Radio synthesis imaging of spiral galaxies
We present results from 21 cm radio synthesis imaging of 28 spiral galaxies
from the DiskMass Survey obtained with the VLA, WSRT, and GMRT facilities. We
detail the observations and data reduction procedures and present a brief
analysis of the radio data. We construct 21 cm continuum images, global HI
emission-line profiles, column-density maps, velocity fields, and
position-velocity diagrams. From these we determine star formation rates
(SFRs), HI line widths, total HI masses, rotation curves, and
azimuthally-averaged radial HI column-density profiles. All galaxies have an HI
disk that extends beyond the readily observable stellar disk, with an average
ratio and scatter of R_{HI}/R_{25}=1.35+/-0.22, and a majority of the galaxies
appear to have a warped HI disk. A tight correlation exists between total HI
mass and HI diameter, with the largest disks having a slightly lower average
column density. Galaxies with relatively large HI disks tend to exhibit an
enhanced stellar velocity dispersion at larger radii, suggesting the influence
of the gas disk on the stellar dynamics in the outer regions of disk galaxies.
We find a striking similarity among the radial HI surface density profiles,
where the average, normalized radial profile of the late-type spirals is
described surprisingly well with a Gaussian profile. These results can be used
to estimate HI surface density profiles in galaxies that only have a total HI
flux measurement. We compare our 21 cm radio continuum luminosities with 60
micron luminosities from IRAS observations for a subsample of 15 galaxies and
find that these follow a tight radio-infrared relation, with a hint of a
deviation from this relation at low luminosities. We also find a strong
correlation between the average SFR surface density and the K-band surface
brightness of the stellar disk.Comment: 22 pages + Appendix, 16 figures + Atlas, 5 tables. Accepted for
publication in Astronomy & Astrophysic
The DiskMass Survey. VIII. On the Relationship Between Disk Stability and Star Formation
We study the relationship between the stability level of late-type galaxy
disks and their star-formation activity using integral-field gaseous and
stellar kinematic data. Specifically, we compare the two-component (gas+stars)
stability parameter from Romeo & Wiegert (Q_RW), incorporating stellar
kinematic data for the first time, and the star-formation rate estimated from
21cm continuum emission. We determine the stability level of each disk
probabilistically using a Bayesian analysis of our data and a simple dynamical
model. Our method incorporates the shape of the stellar velocity ellipsoid
(SVE) and yields robust SVE measurements for over 90% of our sample. Averaging
over this subsample, we find a meridional shape of sigma_z/sigma_R =
0.51^{+0.36}_{-0.25} for the SVE and, at 1.5 disk scale lengths, a stability
parameter of Q_RW = 2.0 +/- 0.9. We also find that the disk-averaged
star-formation-rate surface density (Sigma-dot_e,*) is correlated with the
disk-averaged gas and stellar mass surface densities (Sigma_e,g and Sigma_e,*)
and anti-correlated with Q_RW. We show that an anti-correlation between
Sigma-dot_e,* and Q_RW can be predicted using empirical scaling relations, such
that this outcome is consistent with well-established statistical properties of
star-forming galaxies. Interestingly, Sigma-dot_e,* is not correlated with the
gas-only or star-only Toomre parameters, demonstrating the merit of calculating
a multi-component stability parameter when comparing to star-formation
activity. Finally, our results are consistent with the Ostriker et al. model of
self-regulated star-formation, which predicts
Sigma-dot_e,*/Sigma_e,g/sqrt(Sigma_e,*). Based on this and other theoretical
expectations, we discuss the possibility of a physical link between disk
stability level and star-formation rate in light of our empirical results.Comment: Accepted for publication in ApJ. 15 pages, 6 figures, 2 tables. An
electronic version of Table 1 is available by request, or at
http://www.astro.rug.nl/~westfall/research/dmVIII_table1.tx
The Data Analysis Pipeline for the SDSS-IV MaNGA IFU Galaxy Survey: Emission-Line Modeling
SDSS-IV MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is the
largest integral-field spectroscopy survey to date, aiming to observe a
statistically representative sample of 10,000 low-redshift galaxies. In this
paper we study the reliability of the emission-line fluxes and kinematic
properties derived by the MaNGA Data Analysis Pipeline (DAP). We describe the
algorithmic choices made in the DAP with regards to measuring emission-line
properties, and the effect of our adopted strategy of simultaneously fitting
the continuum and line emission. The effect of random errors are quantified by
studying various fit-quality metrics, idealized recovery simulations and repeat
observations. This analysis demonstrates that the emission lines are well-fit
in the vast majority of the MaNGA dataset and the derived fluxes and errors are
statistically robust. The systematic uncertainty on emission-line properties
introduced by the choice of continuum templates is also discussed. In
particular, we test the effect of using different stellar libraries and simple
stellar-population models on the derived emission-line fluxes and the effect of
introducing different tying prescriptions for the emission-line kinematics. We
show that these effects can generate large ( 0.2 dex) discrepancies at low
signal-to-noise and for lines with low equivalent width (EW); however, the
combined effect is noticeable even for H EW 6~\AA. We provide
suggestions for optimal use of the data provided by SDSS data release 15 and
propose refinements on the \DAP\ for future MaNGA data releases.Comment: accepted on A
SDSS-IV MaNGA: Radial Gradients in Stellar Population Properties of Early-Type and Late-Type Galaxies
We derive ages, metallicities, and individual element abundances of early-
and late-type galaxies (ETGs and LTGs) out to 1.5 R. We study a large
sample of 1900 galaxies spanning in stellar mass,
through key absorption features in stacked spectra from the SDSS-IV/MaNGA
survey. We use mock galaxy spectra with extended star formation histories to
validate our method for LTGs and use corrections to convert the derived ages
into luminosity- and mass-weighted quantities. We find flat age and negative
metallicity gradients for ETGs and negative age and negative metallicity
gradients for LTGs. Age gradients in LTGs steepen with increasing galaxy mass,
from Gyr/R for the lowest mass galaxies to
Gyr/R for the highest mass ones. This strong
gradient-mass relation has a slope of . Comparing local age and
metallicity gradients with the velocity dispersion within galaxies
against the global relation with shows that internal processes
regulate metallicity in ETGs but not age, and vice versa for LTGs. We further
find that metallicity gradients with respect to local show a much
stronger dependence on galaxy mass than radial metallicity gradients. Both
galaxy types display flat [C/Fe] and [Mg/Fe], and negative [Na/Fe] gradients,
whereas only LTGs display gradients in [Ca/Fe] and [Ti/Fe]. ETGs have
increasingly steep [Na/Fe] gradients with local reaching
dex/ km/s for the highest masses. [Na/Fe] ratios are correlated with
metallicity for both galaxy types across the entire mass range in our sample,
providing support for metallicity dependent supernova yields.Comment: 21 pages, 21 figures, 4 tables + Appendi
Patterns and rates of viral evolution in HIV-1 subtype B infected females and males.
Biological sex differences affect the course of HIV infection, with untreated women having lower viral loads compared to their male counterparts but, for a given viral load, women have a higher rate of progression to AIDS. However, the vast majority of data on viral evolution, a process that is clearly impacted by host immunity and could be impacted by sex differences, has been derived from men. We conducted an intensive analysis of HIV-1 gag and env-gp120 evolution taken over the first 6-11 years of infection from 8 Women's Interagency HIV Study (WIHS) participants who had not received combination antiretroviral therapy (ART). This was compared to similar data previously collected from men, with both groups infected with HIV-1 subtype B. Early virus populations in men and women were generally homogenous with no differences in diversity between sexes. No differences in ensuing nucleotide substitution rates were found between the female and male cohorts studied herein. As previously reported for men, time to peak diversity in env-gp120 in women was positively associated with time to CD4+ cell count below 200 (P = 0.017), and the number of predicted N-linked glycosylation sites generally increased over time, followed by a plateau or decline, with the majority of changes localized to the V1-V2 region. These findings strongly suggest that the sex differences in HIV-1 disease progression attributed to immune system composition and sensitivities are not revealed by, nor do they impact, global patterns of viral evolution, the latter of which proceeds similarly in women and men
The Link Between Light and Mass in Late-type Spiral Galaxy Disks
We present the correlation between the extrapolated central disk surface
brightness (mu) and extrapolated central surface mass density (Sigma) for
galaxies in the DiskMass sample. This mu-Sigma-relation has a small scatter of
30% at the high-surface-brightness (HSB) end. At the low surface brightness
(LSB) end, galaxies fall above the mu-Sigma-relation, which we attribute to
their higher dark matter content. After correcting for the dark matter, as well
as for the contribution of gas and the effects of radial gradients in the disk,
the LSB end falls back on the linear mu-Sigma-relation. The resulting scatter
about the corrected mu-Sigma-relation is 25% at the HSB end, and about 50% at
the LSB end. The intrinsic scatter in the mu-Sigma-relation is estimated to be
10% to 20%. Thus, if the surface brightness is known, the stellar surface mass
density is known to within 10-20% (random error). Assuming disks have an
exponential vertical distribution of mass, the average (M_L)_K is 0.24
Msun/Lsun, with an intrinsic scatter around the mean of at most 0.05 Msun/Lsun.
This value for (M/L)_K is 20% smaller than we found in Martinsson et al.,
mainly due to the correction for dark matter applied here. This small scatter
means that among the galaxies in our sample variations in scale height,
vertical density profile shape, and/or the ratio of vertical over radial
velocity dispersion must be small.Comment: Accepted for publication in ApJ Letter
The DiskMass Survey. I. Overview
We present a survey of the mass surface-density of spiral disks, motivated by
outstanding uncertainties in rotation-curve decompositions. Our method exploits
integral-field spectroscopy to measure stellar and gas kinematics in nearly
face-on galaxies sampled at 515, 660, and 860 nm, using the custom-built
SparsePak and PPak instruments. A two-tiered sample, selected from the UGC,
includes 146 nearly face-on galaxies, with B<14.7 and disk scale-lengths
between 10 and 20 arcsec, for which we have obtained H-alpha velocity-fields;
and a representative 46-galaxy subset for which we have obtained stellar
velocities and velocity dispersions. Based on re-calibration of extant
photometric and spectroscopic data, we show these galaxies span factors of 100
in L(K) (0.03 < L/L(K)* < 3), 8 in L(B)/L(K), 10 in R-band disk central
surface-brightness, with distances between 15 and 200 Mpc. The survey is
augmented by 4-70 micron Spitzer IRAC and MIPS photometry, ground-based
UBVRIJHK photometry, and HI aperture-synthesis imaging. We outline the
spectroscopic analysis protocol for deriving precise and accurate line-of-sight
stellar velocity dispersions. Our key measurement is the dynamical disk-mass
surface-density. Star-formation rates and kinematic and photometric regularity
of galaxy disks are also central products of the study. The survey is designed
to yield random and systematic errors small enough (i) to confirm or disprove
the maximum-disk hypothesis for intermediate-type disk galaxies, (ii) to
provide an absolute calibration of the stellar mass-to-light ratio well below
uncertainties in present-day stellar-population synthesis models, and (iii) to
make significant progress in defining the shape of dark halos in the inner
regions of disk galaxies.Comment: To appear in ApJ; 72 pages, 3 tables, 18 figures. High-resolution
version available at
http://www.astro.wisc.edu/~mab/publications/DMS_I_preprint.pd
The DiskMass Survey. II. Error Budget
We present a performance analysis of the DiskMass Survey. The survey uses
collisionless tracers in the form of disk stars to measure the surface-density
of spiral disks, to provide an absolute calibration of the stellar
mass-to-light ratio, and to yield robust estimates of the dark-matter halo
density profile in the inner regions of galaxies. We find a disk inclination
range of 25-35 degrees is optimal for our measurements, consistent with our
survey design to select nearly face-on galaxies. Uncertainties in disk
scale-heights are significant, but can be estimated from radial scale-lengths
to 25% now, and more precisely in the future. We detail the spectroscopic
analysis used to derive line-of-sight velocity dispersions, precise at low
surface-brightness, and accurate in the presence of composite stellar
populations. Our methods take full advantage of large-grasp integral-field
spectroscopy and an extensive library of observed stars. We show that the
baryon-to-total mass fraction (F_b) is not a well-defined observational
quantity because it is coupled to the halo mass model. This remains true even
when the disk mass is known and spatially-extended rotation curves are
available. In contrast, the fraction of the rotation speed supplied by the disk
at 2.2 scale lengths (disk maximality) is a robust observational indicator of
the baryonic disk contribution to the potential. We construct the error-budget
for the key quantities: dynamical disk mass surface-density, disk stellar
mass-to-light ratio, and disk maximality (V_disk / V_circular). Random and
systematic errors in these quantities for individual galaxies will be ~25%,
while survey precision for sample quartiles are reduced to 10%, largely devoid
of systematic errors outside of distance uncertainties.Comment: To appear in ApJ; 88 pages, 4 tables, 18 figures. High-resolution
version available at
http://www.astro.wisc.edu/~mab/publications/DMS_II_preprint.pd
SDSS-IV MaNGA: local and global chemical abundance patterns in early-type galaxies
Chemical enrichment signatures strongly constrain galaxy formation and
evolution, and a detailed understanding of abundance patterns provides clues
regarding the nucleosynthetic production pathways of elements. Using the
SDSS-IV MaNGA IFU survey, we study radial gradients of chemical element
abundances in detail. We use stacked spectra out to 1 Re of 366 early-type
galaxies with masses 9.9 - 10.8 log to probe the abundances of
the elements C, N, Na, Mg, Ca, and Ti, relative to the abundance of Fe, by
fitting stellar population models to a combination of Lick absorption indices.
We find that C, Mg, and Ti trace each other both as a function of galaxy radius
and galaxy mass. These similar C and Mg abundances within and across galaxies
set a lower limit for star-formation timescales. Conversely, N and Ca are
generally offset to lower abundances. The under-abundance of Ca compared to Mg
implies delayed enrichment of Ca through Type Ia supernovae, whereas the
correlated behaviour of Ti and the lighter elements, C and Mg, suggest
contributions to Ti from Type II supernovae. We obtain shallow radial gradients
in [Mg/Fe], [C/Fe], and [Ti/Fe], meaning that these inferences are independent
of radius. However, we measure strong negative radial gradients for [N/Fe] and
[Na/Fe], of up to and dex/Re respectively. These
gradients become shallower with decreasing galaxy mass. We find that N and Na
abundances increase more steeply with velocity dispersion within galaxies than
globally, while the other elements show the same relation locally and globally.
This implies that the high Na and N abundances found in massive early type
galaxies are generated by internal processes within galaxies. These are
strongly correlated with the total metallicity, suggesting
metallicity-dependent Na enrichment, and secondary N production in massive
early-type galaxies.Comment: 17 pages, 9 figures, 4 tables. MNRAS in pres
The DiskMass Survey. IV. The Dark-Matter-Dominated Galaxy UGC 463
We present a detailed and unique mass budget for the high-surface-brightness
galaxy UGC 463, showing it is dominated by dark matter (DM) at radii beyond one
scale length (h_R) and has a baryonic-to-DM mass ratio of approximately 1:3
within 4.2 h_R. Assuming a constant scale height (h_z, calculated via an
empirical oblateness relation), we calculate dynamical disk mass surface
densities from stellar kinematics, which provide vertical velocity dispersions
after correcting for the shape of the stellar velocity ellipsoid (measured to
have sigma_theta/sigma_R=1.04 +/- 0.22 and sigma_z/sigma_R=0.48 +/- 0.09). We
isolate the stellar mass surface density by accounting for all gas mass
components and find an average K-band mass-to-light ratio of 0.22 +/- 0.09
(ran) ^{+0.16}_{-0.15} (sys) M_{sun}/L_{sun}^{K}; Zibetti et al. and Bell et
al. predict, respectively, 0.56 and 3.6 times our dynamical value based on
stellar-population-synthesis modeling. The baryonic matter is submaximal by a
factor of ~3 in mass and the baryonic-to-total circular-speed ratio is
0.61^{+0.07}_{-0.09} (ran) ^{+0.12}_{-0.18} (sys) at 2.2 h_R; however, the disk
is globally stable with a multi-component stability that decreases
asymptotically with radius to Q~2. We directly calculate the circular speed of
the DM halo by subtracting the baryonic contribution to the total circular
speed; the result is equally well described by either a Navarro-Frenk-White
halo or a pseudo-isothermal sphere. The volume density is dominated by DM at
heights of |z|>1.6 h_z for radii of R > h_R. As is shown in follow-up papers,
UGC 463 is just one example among nearly all galaxies we have observed that
contradict the hypothesis that high-surface-brightness spiral galaxies have
maximal disks.Comment: accepted for publication in ApJ (36 pages, 20 figures, 9 tables
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