13 research outputs found
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
Nuclear Rings in Galaxies---A Kinematic Perspective
We combine DensePak integral field unit and TAURUS Fabry-Perot observations
of 13 nuclear rings to show an interconnection between the kinematic properties
of the rings and their resonant origin. The nuclear rings have regular and
symmetric kinematics, and lack strong non-circular motions. This symmetry,
coupled with a direct relationship between the position angles and
ellipticities of the rings and those of their host galaxies, indicate the rings
are in the same plane as the disc and are circular. From the rotation curves
derived, we have estimated the compactness (v^2/r) up to the turnover radius,
which is where the nuclear rings reside. We find that there is evidence of a
correlation between compactness and ring width and size. Radially wide rings
are less compact, and thus have lower mass concentration. The compactness
increases as the ring width decreases. We also find that the nuclear ring size
is dependent on the bar strength, with weaker bars allowing rings of any size
to form.Comment: 19 pages, 7 figures, accepted for publication into Ap
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. 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
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb
Space Telescope (JWST), as determined from the six month commissioning period.
We summarize the performance of the spacecraft, telescope, science instruments,
and ground system, with an emphasis on differences from pre-launch
expectations. Commissioning has made clear that JWST is fully capable of
achieving the discoveries for which it was built. Moreover, almost across the
board, the science performance of JWST is better than expected; in most cases,
JWST will go deeper faster than expected. The telescope and instrument suite
have demonstrated the sensitivity, stability, image quality, and spectral range
that are necessary to transform our understanding of the cosmos through
observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures;
https://iopscience.iop.org/article/10.1088/1538-3873/acb29