63 research outputs found
Evidence for the concurrent growth of thick discs and central mass concentrations from SG imaging
We have produced vertically integrated radial
luminosity profiles of 69 edge-on galaxies from the Spitzer Survey of Stellar
Structure in Galaxies (SG). We decomposed the luminosity profiles into a
disc and a central mass concentration (CMC). These fits, combined with
thin/thick disc decompositions from our previous studies, allow us to estimate
the masses of the CMCs, the thick discs, and the thin discs (, , and ). We obtained atomic
disc masses () from the literature. We then consider the
CMC and the thick disc to be dynamically hot components and the thin disc and
the gas disc to be dynamically cold components. We find that the ratio between
the mass of the hot components and that of the cold components,
, does not depend on the total galaxy mass as described
by circular velocities (). We also find that the higher the , the more concentrated the hot component of a galaxy. We suggest that our
results are compatible with having CMCs and thick discs built in a short and
early high star forming intensity phase. These components were born thick
because of the large scale height of the turbulent gas disc in which they
originated. Our results indicate that the ratio between the star forming rate
in the former phase and that of the formation of the thin disc is of the order
of 10, but the value depends on the duration of the high star forming intensity
phase.Comment: Accepted for publication in A&
The Tully-Fisher relation and the Bosma effect
We show that the rotation curves of 16 nearby disc galaxies in the THINGS
sample and the Milky Way can be described by the NFW halo model and by the
Bosma effect at approximately the same level of accuracy. The latter effect
suggests that the behavior of the rotation curve at large radii is determined
by the rescaled gas component and thus that dark matter and gas distributions
are tightly correlated. By focusing on galaxies with exponential decay in their
gas surface density, we can normalize their rotation curves to match the
exponential thin disc model at large enough radii. This normalization assumes
that the galaxy mass is estimated consistently within this model, assuming a
thin disc structure. We show that this rescaling allows us to derive a new
version of the Tully-Fisher (TF) relation, the Bosma TF relation that nicely
fit the data. In the framework of this model, the connection between the Bosma
Tully-Fisher (TF) relation and the baryonic TF relation can be established by
considering an additional empirical relation between the baryonic mass and the
total mass of the disc, as measured in the data.Comment: 21 pages, 12 figures. Monthly Notices of the Royal Astronomical
Society, in the pres
The distribution of star formation in galactic bars as seen with H and stacked GALEX UV imaging
We investigate the spatial distribution of star formation (SF) within bars of
nearby disk galaxies (inclination ) from the SG survey. We
use archival GALEX far- and near-UV imaging for 772 barred galaxies. We also
assemble a compilation of continuum-subtracted H images for 433 barred
galaxies, of which 70 are produced by ourselves from ancillary photometry and
MUSE/CALIFA IFU data cubes. We employ two complementary approaches: i) the
analysis of bar/disk stacks built from co-added UV images of hundreds of
galaxies; and ii) the classification of the morphology of ionised regions in
galaxies into three main SF classes: A) only circumnuclear SF, B) SF at the bar
ends, but not along the bar, and C) SF along the bar. Lenticular galaxies
typically belong to SF class A: this is probably related to bar-induced SF
quenching. The distribution of SF class B peaks for early- and
intermediate-type spirals: this most likely results from the interplay of gas
flow, shocks, and enhanced shear in centrally concentrated galaxies with large
bar amplitudes. Late-type galaxies are mainly assigned to SF class C: we argue
that this is a consequence of low shear. In bar stacks of spirals, the UV
emission traces the stellar bars and dominates on their leading side, as
witnessed in simulations. For early-types, the central UV emission is 0.5
mag brighter in strongly barred galaxies, relative to their weakly barred
counterparts: this is related to the efficiency of strong bars sweeping the
disk gas and triggering central starbursts. We also show that the distributions
of SF in inner ringed galaxies are broadly the same in barred and non-barred
galaxies, including a UV/H deficit in the middle part of the bar: this
hints at the effect of resonance rings trapping gas. Distinct distributions of
SF within bars are reported in galaxies of different morphological types
(Abridged).Comment: Accepted for publication in A&A (September 2, 2020). 18 pages, 14
figures, 2 tables, plus appendices (16 pages, 8 figures, 1 table
Varied origins of up-bending breaks in galaxy disks
Aims. Using a sample of 175 low-inclination galaxies from the S(4)G, we investigate the origins of up-bending (Type III) breaks in the 3.6 mu m surface brightness profiles of disk galaxies.Methods. We reanalyzed a sample of previously identified Type III disk break-hosting galaxies using a new, unbiased break-finding algorithm, which uncovered many new, sometimes subtle disk breaks across the whole sample. We classified each break by its likely origin through close examination of the galaxy images across wavelengths, and compare samples of galaxies separated by their outermost identified break types in terms of their stellar populations and local environments.Results. We find that more than half of the confirmed Type III breaks in our sample can be attributed to morphological asymmetry in the host galaxies. As these breaks are mostly an artifact of the azimuthal averaging process, their status as physical breaks is questionable. Such galaxies occupy some of the highest density environments in our sample, implying that much of this asymmetry is the result of tidal disturbance. We also find that Type III breaks related to extended spiral arms or star formation often host down-bending (Type II) breaks at larger radius which were previously unidentified. Such galaxies reside in the lowest density environments in our sample, in line with previous studies that found a lack of Type II breaks in clusters. Galaxies occupying the highest density environments most often show Type III breaks associated with outer spheroidal components.Conclusions. We find that Type III breaks in the outer disks of galaxies arise most often through environmental influence: either tidal disturbance (resulting in disk asymmetry) or heating through, for example, galaxy harrassment (leading to spheroidal components). Galaxies hosting the latter break types also show bimodal distributions in central g - r color and morphological type, with more than half of such galaxies classified as Sa or earlier; this suggests these galaxies may be evolving into early-type galaxies. By contrast, we find that Type III breaks related to apparently secular features (e.g., spiral arms) may not truly define their hosts' outer disks, as often in such galaxies additional significant breaks can be found at larger radius. Given this variety in Type III break origins, we recommend in future break studies making a more detailed distinction between break subtypes when seeking out, for example, correlations between disk breaks and environment, to avoid mixing unlike physical phenomena.</div
The massive relic galaxy NGC 1277 is dark matter deficient. From dynamical models of integral-field stellar kinematics out to five effective radii
According to the CDM cosmology, present-day galaxies with stellar
masses should contain a sizable fraction of
dark matter within their stellar body. Models indicate that in massive
early-type galaxies (ETGs) dark matter should account for of the
dynamical mass within five effective radii (). Most massive ETGs
have been shaped through a two-phase process: the rapid growth of a compact
core was followed by the accretion of an extended envelope through mergers. The
exceedingly rare galaxies that have avoided the second phase, the so-called
relic galaxies, are thought to be the frozen remains of the massive ETG
population at . The best relic galaxy candidate discovered to date
is NGC 1277, in the Perseus cluster. We used deep integral field GCMS data to
revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to ). By using Jeans anisotropic modelling we find a negligible dark
matter fraction within (; two-sigma
confidence level), which is in tension with the expectation. Since the lack of
an extended envelope would reduce dynamical friction and prevent the accretion
of an envelope, we propose that NGC 1277 lost its dark matter very early or
that it was dark matter deficient ab initio. We discuss our discovery in the
framework of recent proposals suggesting that some relic galaxies may result
from dark matter stripping as they fell in and interacted within galaxy
clusters. Alternatively, NGC 1277 might have been born in a high-velocity
collision of gas-rich proto-galactic fragments, where dark matter left behind a
disc of dissipative baryons. We speculate that the relative velocities of
required for the latter process to happen were
possible in the progenitors of the present-day rich galaxy clusters.Comment: Accepted for publication in A&
The Thick Disk in the Galaxy NGC 4244 from S^4G Imaging
If thick disks are ubiquitous and a natural product of disk galaxy formation and/or evolution processes, all
undisturbed galaxies that have evolved during a significant fraction of a Hubble time should have a thick disk. The
late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick
disk. Using data from the Spitzer Survey of Stellar Structure in Galaxies (S^4G) we have identified signs of two disk
components in this galaxy. The asymmetries between the light profiles on both sides of the mid-plane of NGC 4244
can be explained by a combination of the galaxy not being perfectly edge-on and a certain degree of opacity of
the thin disk. We argue that the subtlety of the thick disk is a consequence of either a limited secular evolution in
NGC 4244, a small fraction of stellar material in the fragments which built the galaxy, or a high amount of gaseous
accretion after the formation of the galaxy
The Spitzer Survey of Stellar Structure in Galaxies (S^4G)
The Spitzer Survey of Stellar Structure in Galaxies S^4G is an Exploration
Science Legacy Program approved for the Spitzer post-cryogenic mission. It is a
volume-, magnitude-, and size-limited (d < 40 Mpc, |b| > 30 degrees, m_(Bcorr)
< 15.5, D25>1') survey of 2,331 galaxies using IRAC at 3.6 and 4.5 microns.
Each galaxy is observed for 240 s and mapped to > 1.5 x D25. The final
mosaicked images have a typical 1 sigma rms noise level of 0.0072 and 0.0093
MJy / sr at 3.6 and 4.5 microns, respectively. Our azimuthally-averaged surface
brightness profile typically traces isophotes at mu_3.6 (AB) (1 sigma) ~ 27 mag
arcsec^-2, equivalent to a stellar mass surface density of ~ 1 Msun pc^-2. S^4G
thus provides an unprecedented data set for the study of the distribution of
mass and stellar structures in the local Universe. This paper introduces the
survey, the data analysis pipeline and measurements for a first set of
galaxies, observed in both the cryogenic and warm mission phase of Spitzer. For
every galaxy we tabulate the galaxy diameter, position angle, axial ratio,
inclination at mu_3.6 (AB) = 25.5 and 26.5 mag arcsec^-2 (equivalent to ~ mu_B
(AB) =27.2 and 28.2 mag arcsec^-2, respectively). These measurements will form
the initial S^4G catalog of galaxy properties. We also measure the total
magnitude and the azimuthally-averaged radial profiles of ellipticity, position
angle, surface brightness and color. Finally, we deconstruct each galaxy using
GALFIT into its main constituent stellar components: the bulge/spheroid, disk,
bar, and nuclear point source, where necessary. Together these data products
will provide a comprehensive and definitive catalog of stellar structures, mass
and properties of galaxies in the nearby Universe.Comment: Accepted for Publication in PASP, 14 pages, 13 figure
- …