140 research outputs found
The SAMI Galaxy Survey: Revising the Fraction of Slow Rotators in IFS Galaxy Surveys
The fraction of galaxies supported by internal rotation compared to galaxies
stabilized by internal pressure provides a strong constraint on galaxy
formation models. In integral field spectroscopy surveys, this fraction is
biased because survey instruments typically only trace the inner parts of the
most massive galaxies. We present aperture corrections for the two most widely
used stellar kinematic quantities and . Our
demonstration involves integral field data from the SAMI Galaxy Survey and the
ATLAS Survey. We find a tight relation for both and
when measured in different apertures that can be used as a linear
transformation as a function of radius, i.e., a first-order aperture
correction. We find that and radial growth curves are
well approximated by second order polynomials. By only fitting the inner
profile (0.5), we successfully recover the profile out to one
if a constraint between the linear and quadratic parameter in the
fit is applied. However, the aperture corrections for and
derived by extrapolating the profiles perform as well as applying
a first-order correction. With our aperture-corrected
measurements, we find that the fraction of slow rotating galaxies increases
with stellar mass. For galaxies with 11, the fraction
of slow rotators is percent, but is underestimated if galaxies
without coverage beyond one are not included in the sample
( percent). With measurements out to the largest aperture radius
the slow rotator fraction is similar as compared to using aperture corrected
values ( percent). Thus, aperture effects can significantly bias
stellar kinematic IFS studies, but this bias can now be removed with the method
outlined here.Comment: Accepted for Publication in the Monthly Notices of the Royal
Astronomical Society. 16 pages and 11 figures. The key figures of the paper
are: 1, 4, 9, and 1
The SAMI Galaxy Survey: gravitational potential and surface density drive stellar populations -- I. early-type galaxies
The well-established correlations between the mass of a galaxy and the
properties of its stars are considered evidence for mass driving the evolution
of the stellar population. However, for early-type galaxies (ETGs), we find
that color and stellar metallicity [Z/H] correlate more strongly with
gravitational potential than with mass , whereas stellar population
age correlates best with surface density . Specifically, for our sample
of 625 ETGs with integral-field spectroscopy from the SAMI Galaxy Survey,
compared to correlations with mass, the color--, [Z/H]--, and
age-- relations show both smaller scatter and less residual trend with
galaxy size. For the star formation duration proxy [/Fe], we find
comparable results for trends with and , with both being
significantly stronger than the [/Fe]- relation. In determining the
strength of a trend, we analyze both the overall scatter, and the observational
uncertainty on the parameters, in order to compare the intrinsic scatter in
each correlation. These results lead us to the following inferences and
interpretations: (1) the color-- diagram is a more precise tool for
determining the developmental stage of the stellar population than the
conventional color--mass diagram; and (2) gravitational potential is the
primary regulator of global stellar metallicity, via its relation to the gas
escape velocity. Furthermore, we propose the following two mechanisms for the
age and [/Fe] relations with : (a) the age-- and
[/Fe]-- correlations arise as results of compactness driven
quenching mechanisms; and/or (b) as fossil records of the
relation in their disk-dominated progenitors.Comment: 9 pages, 4 figures, 1 table Accepted to Ap
The SAMI Galaxy Survey: Global stellar populations on the size-mass plane
We present an analysis of the global stellar populations of galaxies in the
SAMI Galaxy Survey. Our sample consists of 1319 galaxies spanning four orders
of magnitude in stellar mass and includes all morphologies and environments. We
derive luminosity-weighted, single stellar population equivalent stellar ages,
metallicities and alpha enhancements from spectra integrated within one
effective radius apertures. Variations in galaxy size explain the majority of
the scatter in the age--mass and metallicity--mass relations. Stellar
populations vary systematically in the plane of galaxy size and stellar mass,
such that galaxies with high stellar surface mass density are older, more
metal-rich and alpha-enhanced than less dense galaxies. Galaxies with high
surface mass densities have a very narrow range of metallicities, however, at
fixed mass, the spread in metallicity increases substantially with increasing
galaxy size (decreasing density). We identify residual correlations with
morphology and environment. At fixed mass and size, galaxies with late-type
morphologies, small bulges and low Sersic n are younger than early-type, high
n, high bulge-to-total galaxies. Age and metallicity both show small residual
correlations with environment; at fixed mass and size, galaxies in denser
environments or more massive halos are older and somewhat more metal rich than
those in less dense environments. We connect these trends to evolutionary
tracks within the size--mass plane.Comment: 25 pages, 18 figures, MNRAS in press Corrected typo in author lis
The SAMI Galaxy Survey: mass-kinematics scaling relations
We use data from the Sydney-AAO Multi-object Integral-field spectroscopy
(SAMI) Galaxy Survey to study the dynamical scaling relation between galaxy
stellar mass and the general kinematic parameter that combines rotation velocity and velocity dispersion
. We show that the relation: (1)~is linear above
limits set by properties of the samples and observations; (2)~has slightly
different slope when derived from stellar or gas kinematic measurements;
(3)~applies to both early-type and late-type galaxies and has smaller scatter
than either the Tully-Fisher relation () for late
types or the Faber-Jackson relation () for early types;
and (4)~has scatter that is only weakly sensitive to the value of , with
minimum scatter for in the range 0.4 and 0.7. We compare to the
aperture second moment (the `aperture velocity dispersion') measured from the
integrated spectrum within a 3-arcsecond radius aperture
(). We find that while and
are in general tightly correlated, the relation has less scatter than the relation.Comment: 14 pages, 8 figures, Accepted 2019 May 22. Received 2019 May 18; in
original form 2019 January
A Pair of Compact Red Galaxies at Redshift 2.38, Immersed in a 100 kpc Scale Ly-alpha Nebula
We present Hubble Space Telescope (HST) and ground-based observations of a
pair of galaxies at redshift 2.38, which are collectively known as 2142-4420 B1
(Francis et al. 1996). The two galaxies are both luminous extremely red objects
(EROs), separated by 0.8 arcsec. They are embedded within a 100 kpc scale
diffuse Ly-alpha nebula (or blob) of luminosity ~10^44 erg/s.
The radial profiles and colors of both red objects are most naturally
explained if they are young elliptical galaxies: the most distant yet found. It
is not, however, possible to rule out a model in which they are abnormally
compact, extremely dusty starbursting disk galaxies. If they are elliptical
galaxies, their stellar populations have inferred masses of ~10^11 solar masses
and ages of ~7x10^8 years. Both galaxies have color gradients: their centers
are significantly bluer than their outer regions. The surface brightness of
both galaxies is roughly an order of magnitude greater than would be predicted
by the Kormendy relation. A chain of diffuse star formation extending 1 arcsec
from the galaxies may be evidence that they are interacting or merging.
The Ly-alpha nebula surrounding the galaxies shows apparent velocity
substructure of amplitude ~ 700 km/s. We propose that the Ly-alpha emission
from this nebula may be produced by fast shocks, powered either by a galactic
superwind or by the release of gravitational potential energy.Comment: 33 pages, 9 figures, ApJ in press (to appear in Jun 10 issue
The SAMI pilot survey: The kinematic morphology-density relation in Abell 85, Abell 168 and Abell 2399
We examine the kinematic morphology of early-type galaxies (ETGs) in three galaxy clusters Abell 85, 168 and 2399. Using data from the Sydney-AAOMulti-object Integral field spectrograph we measure spatially resolved kinematics for 79 ETGs in these clusters. We calculate λR, a proxy for the projected specific stellar angular momentum, for each galaxy and classify the 79 ETGs in our samples as fast or slow rotators. We calculate the fraction of slow rotators in the ETG populations (fSR) of the clusters to be 0.21 ± 0.08, 0.08 ± 0.08 and 0.12 ± 0.06 for Abell 85, 168 and 2399, respectively, with an overall fraction of 0.15 ± 0.04. These numbers are broadly consistent with the values found in the literature, confirming recent work asserting that the fraction of slow rotators in the ETG population is constant across many orders of magnitude in global environment. We examine the distribution of kinematic classes in each cluster as a function of environment using the projected density of galaxies: the kinematic morphology-density relation.We find that in Abell 85 fSR increases in higher density regions but in Abell 168 and 2399 this trend is not seen. We examine the differences between the individual clusters to explain this. In addition, we find slow rotators on the outskirts of two of the clusters studied, Abell 85 and 2399. These galaxies reside in intermediate to low density regions and have clearly not formed at the centre of a cluster environment. We hypothesize that they formed at the centres of groups and are falling into the clusters for the first time
The SAMI Galaxy Survey: Decomposed Stellar Kinematics of Galaxy Bulges and Disks
We investigate the stellar kinematics of the bulge and disk components in 826
galaxies with a wide range of morphology from the Sydney-AAO Multi-object
Integral-field spectroscopy (SAMI) Galaxy Survey. The spatially-resolved
rotation velocity (V) and velocity dispersion () of bulge and disk
components have been simultaneously estimated using the penalized pixel fitting
(pPXF) method with photometrically defined weights for the two components. We
introduce a new subroutine of pPXF for dealing with degeneracy in the
solutions. We show that the V and distributions in each galaxy can be
reconstructed using the kinematics and weights of the bulge and disk
components. The combination of two distinct components provides a consistent
description of the major kinematic features of galaxies over a wide range of
morphological types. We present Tully-Fisher and Faber-Jackson relations
showing that the galaxy stellar mass scales with both V and for both
components of all galaxy types. We find a tight Faber-Jackson relation even for
the disk component. We show that the bulge and disk components are
kinematically distinct: (1) the two components show scaling relations with
similar slopes, but different intercepts; (2) the spin parameter
indicates bulges are pressure-dominated systems and disks are supported by
rotation; (3) the bulge and disk components have, respectively, low and high
values in intrinsic ellipticity. Our findings suggest that the relative
contributions of the two components explain, at least to first order, the
complex kinematic behaviour of galaxies.Comment: 22 pages, 21 figures; Accepted for publication in MNRA
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