85 research outputs found
The radial acceleration relation is a natural consequence of the baryonic Tully-Fisher relation
Galaxies covering several orders of magnitude in stellar mass and a variety
of Hubble types have been shown to follow the "Radial Acceleration Relation"
(RAR), a relationship between , the observed circular acceleration
of the galaxy, and , the acceleration due to the total baryonic
mass of the galaxy. For accelerations above ,
traces , asymptoting to the 1:1 line. Below this
scale, there is a break in the relation such that . We show that the RAR slope, scatter and the acceleration scale are
all natural consequences of the well-known baryonic Tully-Fisher relation
(BTFR). We further demonstrate that galaxies with a variety of baryonic and
dark matter (DM) profiles and a wide range of dark halo and galaxy properties
(well beyond those expected in CDM) lie on the RAR if we simply require that
their rotation curves satisfy the BTFR. We explore conditions needed to break
this degeneracy: sub-kpc resolved rotation curves inside of "cored"
DM-dominated profiles and/or outside kpc could lie on BTFR but
deviate in the RAR, providing new constraints on DM.Comment: 5 pages, submitted to MNRA
Hamilton Cycles in Addition Graphs
If A is a square-free subset of an abelian group G, then the addition graph of A on G is the graph with vertex set G and distinct vertices x and y forming an edge if and only if x+y is in A. We prove that every connected cubic addition graph on an abelian group G whose order is divisible by 8 is Hamiltonian as well as every connected bipartite cubic addition graph on an abelian group G whose order is divisible by 4. We show that connected bipartite addition graphs are Cayley graphs and prove that every connected cubic Cayley graph on a group of dihedral type whose order is divisible by 4 is Hamiltonian
The Mass Dependance of Satellite Quenching in Milky Way-like Halos
Using the Sloan Digital Sky Survey, we examine the quenching of satellite
galaxies around isolated Milky Way-like hosts in the local Universe. We find
that the efficiency of satellite quenching around isolated galaxies is low and
roughly constant over two orders of magnitude in satellite stellar mass
( = ), with only of systems
quenched as a result of environmental processes. While largely independent of
satellite stellar mass, satellite quenching does exhibit clear dependence on
the properties of the host. We show that satellites of passive hosts are
substantially more likely to be quenched than those of star-forming hosts, and
we present evidence that more massive halos quench their satellites more
efficiently. These results extend trends seen previously in more massive host
halos and for higher satellite masses. Taken together, it appears that galaxies
with stellar masses larger than about are uniformly
resistant to environmental quenching, with the relative harshness of the host
environment likely serving as the primary driver of satellite quenching. At
lower stellar masses (), however, observations of the Local
Group suggest that the vast majority of satellite galaxies are quenched,
potentially pointing towards a characteristic satellite mass scale below which
quenching efficiency increases dramatically.Comment: 14 pages, 8 figure
Environmental Quenching of Low-Mass Field Galaxies
In the local Universe, there is a strong division in the star-forming
properties of low-mass galaxies, with star formation largely ubiquitous amongst
the field population while satellite systems are predominantly quenched. This
dichotomy implies that environmental processes play the dominant role in
suppressing star formation within this low-mass regime (). As shown by observations of the Local Volume,
however, there is a non-negligible population of passive systems in the field,
which challenges our understanding of quenching at low masses. By applying the
satellite quenching models of Fillingham et al. (2015) to subhalo populations
in the Exploring the Local Volume In Simulations (ELVIS) suite, we investigate
the role of environmental processes in quenching star formation within the
nearby field. Using model parameters that reproduce the satellite quenched
fraction in the Local Group, we predict a quenched fraction -- due solely to
environmental effects -- of within
of the Milky Way and M31. This is in good agreement with current observations
of the Local Volume and suggests that the majority of the passive field systems
observed at these distances are quenched via environmental mechanisms. Beyond
, however, dwarf galaxy quenching becomes difficult to explain
through an interaction with either the Milky Way or M31, such that more
isolated, field dwarfs may be self-quenched as a result of star-formation
feedback.Comment: 9 pages, 4 figures, MNRAS accepted version, comments welcome - RIP
Ducky...gone but never forgotte
A Dichotomy in Satellite Quenching Around L* Galaxies
We examine the star formation properties of bright (~0.1 L*) satellites
around isolated ~L* hosts in the local Universe using spectroscopically
confirmed systems in the Sloan Digital Sky Survey DR7. Our selection method is
carefully designed with the aid of N-body simulations to avoid groups and
clusters. We find that satellites are significantly more likely to be quenched
than a stellar mass-matched sample of isolated galaxies. Remarkably, this
quenching occurs only for satellites of hosts that are themselves quenched:
while star formation is unaffected in the satellites of star-forming hosts,
satellites around quiescent hosts are more than twice as likely to be quenched
than stellar-mass matched field samples. One implication of this is that
whatever shuts down star formation in isolated, passive L* galaxies also plays
at least an indirect role in quenching star formation in their bright
satellites. The previously-reported tendency for "galactic conformity" in
color/morphology may be a by-product of this host-specific quenching dichotomy.
The S\'ersic indices of quenched satellites are statistically identical to
those of field galaxies with the same specific star formation rates, suggesting
that environmental and secular quenching give rise to the same morphological
structure. By studying the distribution of pairwise velocities between the
hosts and satellites, we find dynamical evidence that passive host galaxies
reside in dark matter halos that are ~45% more massive than those of
star-forming host galaxies of the same stellar mass. We emphasize that even
around passive hosts, the mere fact that galaxies become satellites does not
typically result in star formation quenching: we find that only ~30% of ~0.1 L*
galaxies that fall in from the field are quenched around passive hosts,
compared with ~0% around star forming hosts.Comment: 14 pages, 9 figure
Taking Care of Business in a Flash: Constraining the Timescale for Low-Mass Satellite Quenching with ELVIS
The vast majority of dwarf satellites orbiting the Milky Way and M31 are
quenched, while comparable galaxies in the field are gas-rich and star-forming.
Assuming that this dichotomy is driven by environmental quenching, we use the
ELVIS suite of N-body simulations to constrain the characteristic timescale
upon which satellites must quench following infall into the virial volumes of
their hosts. The high satellite quenched fraction observed in the Local Group
demands an extremely short quenching timescale (~ 2 Gyr) for dwarf satellites
in the mass range Mstar ~ 10^6-10^8 Msun. This quenching timescale is
significantly shorter than that required to explain the quenched fraction of
more massive satellites (~ 8 Gyr), both in the Local Group and in more massive
host halos, suggesting a dramatic change in the dominant satellite quenching
mechanism at Mstar < 10^8 Msun. Combining our work with the results of
complementary analyses in the literature, we conclude that the suppression of
star formation in massive satellites (Mstar ~ 10^8 - 10^11 Msun) is broadly
consistent with being driven by starvation, such that the satellite quenching
timescale corresponds to the cold gas depletion time. Below a critical stellar
mass scale of ~ 10^8 Msun, however, the required quenching times are much
shorter than the expected cold gas depletion times. Instead, quenching must act
on a timescale comparable to the dynamical time of the host halo. We posit that
ram-pressure stripping can naturally explain this behavior, with the critical
mass (of Mstar ~ 10^8 Msun) corresponding to halos with gravitational restoring
forces that are too weak to overcome the drag force encountered when moving
through an extended, hot circumgalactic medium.Comment: 12 pages, 6 figures; resubmitted to MNRAS after referee report
(August 25, 2015
Under Pressure: Quenching Star Formation in Low-Mass Satellite Galaxies via Stripping
Recent studies of galaxies in the local Universe, including those in the
Local Group, find that the efficiency of environmental (or satellite) quenching
increases dramatically at satellite stellar masses below ~ . This suggests a physical scale where quenching transitions from a
slow "starvation" mode to a rapid "stripping" mode at low masses. We
investigate the plausibility of this scenario using observed HI surface density
profiles for a sample of 66 nearby galaxies as inputs to analytic calculations
of ram-pressure and viscous stripping. Across a broad range of host properties,
we find that stripping becomes increasingly effective at $M_{*} < 10^{8-9}\
{\rm M}_{\odot}n_{\rm halo} <
10^{-3.5}{\rm cm}^{-3}$), we find that stripping is not fully effective;
infalling satellites are, on average, stripped of < 40 - 70% of their cold gas
reservoir, which is insufficient to match observations. By including a host
halo gas distribution that is clumpy and therefore contains regions of higher
density, we are able to reproduce the observed HI gas fractions (and thus the
high quenched fraction and short quenching timescale) of Local Group
satellites, suggesting that a host halo with clumpy gas may be crucial for
quenching low-mass systems in Local Group-like (and more massive) host halos.Comment: updated version after review, now accepted to MNRAS; Accepted 2016
August 22. Received 2016 August 18; in original form 2016 June 2
Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites
We present FIRE/Gizmo hydrodynamic zoom-in simulations of isolated dark
matter halos, two each at the mass of classical dwarf galaxies () and ultra-faint galaxies (), and with two feedback implementations. The resultant central
galaxies lie on an extrapolated abundance matching relation from to without a break. Every host is filled with
subhalos, many of which form stars. Our dwarfs with each have 1-2 well-resolved satellites with . Even our isolated ultra-faint galaxies have
star-forming subhalos. If this is representative, dwarf galaxies throughout the
universe should commonly host tiny satellite galaxies of their own. We combine
our results with the ELVIS simulations to show that targeting regions around nearby isolated dwarfs could increase the chances of
discovering ultra-faint galaxies by compared to random halo
pointings, and specifically identify the region around the Phoenix dwarf galaxy
as a good potential target.
The well-resolved ultra-faint galaxies in our simulations () form within halos. Each has a uniformly ancient stellar population () owing to reionization-related quenching. More massive systems, in
contrast, all have late-time star formation. Our results suggest that is a probable dividing line between halos
hosting reionization "fossils" and those hosting dwarfs that can continue to
form stars in isolation after reionization.Comment: 12 pages, 6 figures, 1 table, submitted to MNRA
Modelling chemical abundance distributions for dwarf galaxies in the Local Group: the impact of turbulent metal diffusion
We investigate stellar metallicity distribution functions (MDFs), including
Fe and -element abundances, in dwarf galaxies from the Feedback in
Realistic Environments (FIRE) project. We examine both isolated dwarf galaxies
and those that are satellites of a Milky Way-mass galaxy. In particular, we
study the effects of including a sub-grid turbulent model for the diffusion of
metals in gas. Simulations that include diffusion have narrower MDFs and
abundance ratio distributions, because diffusion drives individual gas and star
particles toward the average metallicity. This effect provides significantly
better agreement with observed abundance distributions of dwarf galaxies in the
Local Group, including the small intrinsic scatter in [/Fe] vs.
[Fe/H] (less than 0.1 dex). This small intrinsic scatter arises in our
simulations because the interstellar medium (ISM) in dwarf galaxies is
well-mixed at nearly all cosmic times, such that stars that form at a given
time have similar abundances to within 0.1 dex. Thus, most of the scatter in
abundances at z = 0 arises from redshift evolution and not from instantaneous
scatter in the ISM. We find similar MDF widths and intrinsic scatter for
satellite and isolated dwarf galaxies, which suggests that environmental
effects play a minor role compared with internal chemical evolution in our
simulations. Overall, with the inclusion of metal diffusion, our simulations
reproduce abundance distribution widths of observed low-mass galaxies, enabling
detailed studies of chemical evolution in galaxy formation.Comment: 19 pages, 13 figures, published in MNRA
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