186 research outputs found
Choirs, H I galaxy groups: catalogue and detection of star-forming dwarf group members
Hα observations centred on galaxies selected from the H i Parkes All-Sky Survey (HiPASS) typically show one and sometimes two star-forming galaxies within the ∼15 arcmin beam of the Parkes 64 m H i detections. In our Survey for Ionization in Neutral Gas Galaxies (SINGG) we found 15 cases of HiPASS sources containing four or more emission line galaxies (ELGs). We name these fields Choir groups. In the most extreme case, we found a field with at least nine ELGs. In this paper, we present a catalogue of Choir group members in the context of the wider SINGG sample.
The dwarf galaxies in the Choir groups would not be individually detectable in HiPASS at the observed distances if they were isolated, but are detected in SINGG narrow-band imaging due to their membership of groups with sufficiently large total H i mass. The ELGs in these groups are similar to the wider SINGG sample in terms of size, Hα equivalent width and surface brightness.
Eight of these groups have two large spiral galaxies with several dwarf galaxies and may be thought of as morphological analogues of the Local Group. However, on average our groups are not significantly H i deficient, suggesting that they are at an early stage of assembly, and more like the M81 group. The Choir groups are very compact at typically only 190 kpc in projected distance between the two brightest members. They are very similar to SINGG fields in terms of star formation efficiency (SFE; the ratio of star formation rate to H i mass), showing an increasing trend in SFE with stellar mass
The stellar mass - size relation for cluster galaxies at z=1 with high angular resolution from the Gemini/GeMS multi-conjugate adaptive optics system
We present the stellar mass - size relation for 49 galaxies within the =
1.067 cluster SPT-CL J05465345, with FWHM 80-120 mas -band data from the Gemini multi-conjugate adaptive optics system
(GeMS/GSAOI). This is the first such measurement in a cluster environment,
performed at sub-kpc resolution at rest-frame wavelengths dominated by the
light of the underlying old stellar populations. The observed stellar mass -
size relation is offset from the local relation by 0.21 dex, corresponding to a
size evolution proportional to , consistent with the literature.
The slope of the stellar mass - size relation = 0.74 0.06,
consistent with the local relation. The absence of slope evolution indicates
that the amount of size growth is constant with stellar mass. This suggests
that galaxies in massive clusters such as SPT-CL J05465345 grow via
processes that increase the size without significant morphological
interference, such as minor mergers and/or adiabatic expansion. The slope of
the cluster stellar mass - size relation is significantly shallower if measured
in /ACS imaging at wavelengths blueward of the Balmer break, similar to
rest-frame UV relations at = 1 in the literature. The stellar mass - size
relation must be measured at redder wavelengths, which are more sensitive to
the old stellar population that dominates the stellar mass of the galaxies. The
slope is unchanged when GeMS -band imaging is degraded to the resolution
of -band HST/NICMOS resolution but dramatically affected when degraded to
-band Magellan/FourStar resolution. Such measurements must be made with AO
in order to accurately characterise the sizes of compact, = 1 galaxies.Comment: 24 pages, 13 figures, 3 tables. Accepted for publication in MNRAS.
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Angular momentum evolution of bulge stars in disc galaxies in NIHAO
We study the origin of bulge stars and their angular momentum (AM) evolution
in 10 spiral galaxies with baryonic masses above M in the
NIHAO galaxy formation simulations. The simulated galaxies are in good
agreement with observations of the relation between specific AM and mass of the
baryonic component and the stellar bulge-to-total ratio (). We divide the
star particles at into disc and bulge components using a hybrid
photometric/kinematic decomposition method that identifies all central mass
above an exponential disc profile as the `bulge'. By tracking the bulge star
particles back in time, we find that on average 95\% of the bulge stars formed
{\it in situ}, 3\% formed {\it ex situ} in satellites of the same halo, and
only 2\% formed {\it ex situ} in external galaxies. The evolution of the AM
distribution of the bulge stars paints an interesting picture: the higher the
final ratio, the more the specific AM remains preserved during the bulge
formation. In all cases, bulge stars migrate significantly towards the central
region, reducing their average galactocentric radius by roughly a factor 2,
independently of the final value. However, in the higher
() objects, the velocity of the bulge stars increases and the AM of
the bulge is almost conserved, whereas at lower values, the velocity of
the bulge stars decreases and the AM of bulge reduces. The correlation between
the evolution of the AM and suggests that bulge and disc formation are
closely linked and cannot be treated as independent processes.Comment: 17 pages, 16 Figures, 1 table; accepted for publication in MNRA
Dynamic equilibrium sets atomic content of galaxies across cosmic time
We analyze 88 independent high-resolution cosmological zoom-in simulations of
disk galaxies in the NIHAO simulations suite to explore the connection between
the atomic gas fraction and angular momentum of baryons throughout cosmic time.
The study is motivated by the analytic model of \citet{obreschkow16}, which
predicts a relation between the atomic gas fraction and the
global atomic stability parameter , where and
are the mass and specific angular momentum of the galaxy (stars+cold gas) and
is the velocity dispersion of the atomic gas. We show that the
simulated galaxies follow this relation from their formation () to
present within dex. To explain this behavior, we explore the
evolution of the local Toomre stability and find that -- of the
atomic gas in all simulated galaxies is stable at any time. In other words,
throughout the entire epoch of peak star formation until today, the timescale
for accretion is longer than the timescale to reach equilibrium, thus resulting
in a quasi-static equilibrium of atomic gas at any time. Hence, the evolution
of depends on the complex hierarchical growth history primarily
via the evolution of . An exception are galaxies subject to strong
environmental effects.Comment: 12 pages, 7 figures; accepted to Ap
Revisiting the stellar mass -- angular momentum -- morphology relation: extension to higher bulge fraction, and the effect of bulge type
We present the relation between stellar specific angular momentum ,
stellar mass , and bulge-to-total light ratio for THINGS, CALIFA
and Romanowsky \& Fall datasets, exploring the existence of a fundamental plane
between these parameters as first suggested by Obreschkow \& Glazebrook. Our
best-fit relation yields a slope of with a
trivariate fit including . When ignoring the effect of , the
exponent is consistent with predicted
for dark matter halos. There is a linear relation for , exhibiting a general trend of increasing with decreasing
. Galaxies with have higher than predicted
by the relation. Pseudobulge galaxies have preferentially lower for a
given than galaxies that contain classical bulges. Pseudobulge
galaxies follow a well-defined track in space, consistent
with Obreschkow \& Glazebrook, while galaxies with classical bulges do not.
These results are consistent with the hypothesis that while growth in either
bulge type is linked to a decrease in , the mechanisms that build
pseudobulges seem to be less efficient at increasing bulge mass per decrease in
specific angular momentum than those that build classical bulges.Comment: Accepted to ApJ. 10 pages, 3 figures, 2 table
SHDE: Survey description and mass-kinematics scaling relations for dwarf galaxies
The Study of H from Dwarf Emissions (SHDE) is a high spectral
resolution (R=13500) H integral field survey of 69 dwarf galaxies with
stellar masses . The survey used FLAMES on
the ESO Very Large Telescope. SHDE is designed to study the kinematics
and stellar populations of dwarf galaxies using consistent methods applied to
massive galaxies and at matching level of detail, connecting these mass ranges
in an unbiased way. In this paper we set out the science goals of SHDE,
describe the sample properties, outline the data reduction and analysis
processes. We investigate the mass-kinematics
scaling relation, which have previously shown potential for combining galaxies
of all morphologies in a single scaling relation. We extend the scaling
relation from massive galaxies to dwarf galaxies, demonstrating this relation
is linear down to a stellar mass of .
Below this limit, the kinematics of galaxies inside one effective radius appear
to be dominated by the internal velocity dispersion limit of the
H-emitting gas, giving a bend in the
relation. Replacing stellar mass with total baryonic mass using gas mass
estimate reduces the severity but does not remove the linearity limit of the
scaling relation. An extrapolation to estimate the galaxies' dark matter halo
masses, yields a scaling relation that is free of
any bend, has reduced curvature over the whole mass range, and brings galaxies
of all masses and morphologies onto the virial relation.Comment: 19 pages, 13 figures, 5 tables; published in MNRA
Searching for Binary Y Dwarfs with the Gemini Multi-Conjugate Adaptive Optics System (GeMS)
The NASA Wide-field Infrared Survey Explorer (WISE) has discovered almost all the known members of the new class of Y-type brown dwarfs. Most of these Y dwarfs have been identified as isolated objects in the field. It is known that binaries with L- and T-type brown dwarf primaries are less prevalent than either M-dwarf or solar-type primaries, they tend to have smaller separations and are more frequently detected in near-equal mass configurations. The binary statistics for Y-type brown dwarfs, however, are sparse, and so it is unclear if the same trends that hold for L- and T-type brown dwarfs also hold for Y-type ones. In addition, the detection of binary companions to very cool Y dwarfs may well be the best means available for discovering even colder objects. We present results for binary properties of a sample of five WISE Y dwarfs with the Gemini Multi-Conjugate Adaptive Optics System. We find no evidence for binary companions in these data, which suggests these systems are not equal-luminosity (or equal-mass) binaries with separations larger than ~0.5–1.9 AU. For equal-mass binaries at an age of 5 Gyr, we find that the binary binding energies ruled out by our observations (i.e., 10^(42) erg) are consistent with those observed in previous studies of hotter ultra-cool dwarfs
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