22 research outputs found
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
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
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 (M_* ∼ 10^(5.5–8) M_⊙). 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 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 ∼0.52 ± 0.26 within 1 < R/R_(vir) < 2 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 2R_(vir), 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
Discovery and Follow-up Observations of the Young Type Ia Supernova 2016coj
The Type~Ia supernova (SN~Ia) 2016coj in NGC 4125 (redshift ) was
discovered by the Lick Observatory Supernova Search 4.9 days after the fitted
first-light time (FFLT; 11.1 days before -band maximum). Our first detection
(pre-discovery) is merely day after the FFLT, making SN 2016coj one
of the earliest known detections of a SN Ia. A spectrum was taken only 3.7 hr
after discovery (5.0 days after the FFLT) and classified as a normal SN Ia. We
performed high-quality photometry, low- and high-resolution spectroscopy, and
spectropolarimetry, finding that SN 2016coj is a spectroscopically normal SN
Ia, but with a high velocity of \ion{Si}{2} 6355 (\,\kms\
around peak brightness). The \ion{Si}{2} 6355 velocity evolution can
be well fit by a broken-power-law function for up to a month after the FFLT. SN
2016coj has a normal peak luminosity ( mag), and it
reaches a -band maximum \about16.0~d after the FFLT. We estimate there to be
low host-galaxy extinction based on the absence of Na~I~D absorption lines in
our low- and high-resolution spectra. The spectropolarimetric data exhibit weak
polarization in the continuum, but the \ion{Si}{2} line polarization is quite
strong () at peak brightness.Comment: Submitte
The Lick AGN Monitoring Project 2016: Dynamical Modeling of Velocity-Resolved H\b{eta} Lags in Luminous Seyfert Galaxies
We have modeled the velocity-resolved reverberation response of the H\b{eta}
broad emission line in nine Seyfert 1 galaxies from the Lick Active Galactic
Nucleus (AGN) Monitioring Project 2016 sample, drawing inferences on the
geometry and structure of the low-ionization broad-line region (BLR) and the
mass of the central supermassive black hole. Overall, we find that the H\b{eta}
BLR is generally a thick disk viewed at low to moderate inclination angles. We
combine our sample with prior studies and investigate line-profile shape
dependence, such as log10(FWHM/{\sigma}), on BLR structure and kinematics and
search for any BLR luminosity-dependent trends. We find marginal evidence for
an anticorrelation between the profile shape of the broad H\b{eta} emission
line and the Eddington ratio, when using the root-mean-square spectrum.
However, we do not find any luminosity-dependent trends, and conclude that AGNs
have diverse BLR structure and kinematics, consistent with the hypothesis of
transient AGN/BLR conditions rather than systematic trends
The Lick AGN Monitoring Project 2016 : dynamical modeling of velocity-resolved Hβ lags in luminous Seyfert galaxies
K.H. acknowledges support from STFC grant ST/R000824/1.We have modeled the velocity-resolved reverberation response of the Hβ broad emission line in nine Seyfert 1 galaxies from the Lick Active Galactic Nucleus (AGN) Monitoring Project 2016 sample, drawing inferences on the geometry and structure of the low-ionization broad-line region (BLR) and the mass of the central supermassive black hole. Overall, we find that the Hβ BLR is generally a thick disk viewed at low to moderate inclination angles. We combine our sample with prior studies and investigate line-profile shape dependence, such as log10(FWHM/σ), on BLR structure and kinematics and search for any BLR luminosity-dependent trends. We find marginal evidence for an anticorrelation between the profile shape of the broad Hβ emission line and the Eddington ratio, when using the rms spectrum. However, we do not find any luminosity-dependent trends, and conclude that AGNs have diverse BLR structure and kinematics, consistent with the hypothesis of transient AGN/BLR conditions rather than systematic trends.Publisher PDFPeer reviewe
The Lick AGN Monitoring Project 2016 : velocity-resolved Hβ lags in luminous Seyfert galaxies
Funding: K.H. acknowledges support from STFC grant ST/R000824/1.We carried out spectroscopic monitoring of 21 low-redshift Seyfert 1 galaxies using the Kast double spectrograph on the 3 m Shane telescope at Lick Observatory from April 2016 to May 2017. Targetingactive galactic nuclei (AGN) with luminosities of λLλ(5100 Å) ≈ 1044 erg s−1 and predicted Hβ lags of∼ 20–30 days or black hole masses of 107–108.5 M⊙, our campaign probes luminosity-dependent trends in broad-line region (BLR) structure and dynamics as well as to improve calibrations for single-epoch estimates of quasar black hole masses. Here we present the first results from the campaign, including Hβ emission-line light curves, integrated Hβ lag times (8–30 days) measured against V -band continuum light curves, velocity-resolved reverberation lags, line widths of the broad Hβ components, and virial black hole mass estimates (107.1–108.1 M⊙). Our results add significantly to the number of existing velocity-resolved lag measurements and reveal a diversity of BLR gas kinematics at moderately high AGN luminosities. AGN continuum luminosity appears not to be correlated with the type of kinematics that its BLR gas may exhibit. Follow-up direct modeling of this dataset will elucidate the detailed kinematics and provide robust dynamical black hole masses for several objects in this sample.Publisher PDFPeer reviewe