122 research outputs found
Not So Heavy Metals: Black Hole Feedback Enriches The Circumgalactic Medium
We examine the effects of SMBH feedback on the CGM using a cosmological
hydrodynamic simulation \citep[{\sc Romulus25};][]{Tremmel2017} and a set of
four zoom-in `genetically modified' Milky Way-mass galaxies sampling different
evolutionary paths. By tracing the distribution of metals in the circumgalactic
medium (CGM), we show that \ion{O}{6} is a sensitive indicator of supermassive
black hole (SMBH) feedback. First, we calculate the column densities of
\ion{O}{6} in simulated Milky Way-mass galaxies and compare them with
observations from the COS-Halos Survey. Our simulations show column densities
of \ion{O}{6} in the CGM consistent with those of COS-Halos star forming and
quenched galaxies. These results contrast with those from previous simulation
studies which typically underproduce CGM column densities of \ion{O}{6}. We
determine that a galaxy's star formation history and assembly record have
little effect on the amount of \ion{O}{6} in its CGM. Instead, column densities
of \ion{O}{6} are closely tied to galaxy halo mass and BH growth history. The
set of zoom-in, genetically modified Milky Way-mass galaxies indicates that the
SMBH drives highly metal-enriched material out into its host galaxy's halo
which in turn elevates the column densities of \ion{O}{6} in the CGM.Comment: 14 pages, 12 figures, Submitted to ApJ; Note: Figures have
transparency that may not render in browse
One-Two Quench: A Double Minor Merger Scenario
Using the N-body+Smoothed particle hydrodynamics code, ChaNGa, we identify
two merger-driven processes\textemdash disk disruption and supermassive black
hole (SMBH) feedback\textemdash which work together to quench L galaxies
for over 7 Gyr. Specifically, we examine the cessation of star formation in a
simulated Milky Way (MW) analog, driven by an interaction with two minor
satellites. Both interactions occur within 100 Myr of each other, and the
satellites both have masses 5 to 20 times smaller than that of their MW-like
host galaxy. Using the genetic modification process of \cite{Roth2016}, we
generate a set of four zoom-in, MW-mass galaxies all of which exhibit unique
star formation histories due to small changes to their assembly histories. In
two of these four cases, the galaxy is quenched by . Because these are
controlled modifications, we are able to isolate the effects of two
closely-spaced minor merger events, the relative timing of which determines
whether the MW-mass main galaxy quenches. This one-two punch works to: 1. fuel
the primary halo's supermassive black hole (SMBH) at its peak accretion rate;
and 2. disrupt the cold, gaseous disk of the host galaxy. The end result is
that feedback from the SMBH thoroughly and abruptly ends the galaxy's star
formation by . We search for and find a similar quenching event in
{\sc Romulus25}, a hydrodynamical volume simulation,
demonstrating that the mechanism is common enough to occur even in a small
sample of MW-mass quenched galaxies at .Comment: 11 pages, 8 figures, submitted to Ap
Reverberation Mapping of the Kepler-Field AGN KA1858+4850
KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among
the brightest active galaxies monitored by the Kepler mission. We have carried
out a reverberation mapping campaign designed to measure the broad-line region
size and estimate the mass of the black hole in this galaxy. We obtained 74
epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m
telescope from February to November of 2012, and obtained complementary V-band
images from five other ground-based telescopes. We measured the H-beta light
curve lag with respect to the V-band continuum light curve using both
cross-correlation techniques (CCF) and continuum light curve variability
modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53
(+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta
root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s.
Combining these two results and assuming a virial scale factor of f = 5.13, we
obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the
mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also
obtained consistent but slightly shorter emission-line lags with respect to the
Kepler light curve. Thanks to the Kepler mission, the light curve of
KA1858+4850 has among the highest cadences and signal-to-noise ratios ever
measured for an active galactic nucleus; thus, our black hole mass measurement
will serve as a reference point for relations between black hole mass and
continuum variability characteristics in active galactic nuclei
Choirs, HI galaxy groups: Catalogue and detection of star-forming dwarf group members
Hα observations centred on galaxies selected from the HI Parkes All-Sky Survey (HIPASS)typically show one and sometimes two star-forming galaxies within the ~15 arcmin beam of the Parkes 64 m HI detections. In our Survey for Ionization in Neutral Gas Ga
Dust attenuation in disk-dominated galaxies: evidence for the 2175A dust feature
The attenuation of starlight by interstellar dust is investigated in a sample
of low redshift, disk-dominated star-forming galaxies using photometry from
GALEX and SDSS. By considering broadband colors as a function of galaxy
inclination we are able to confidently separate trends arising from increasing
dust opacity from possible differences in stellar populations, since stellar
populations do not correlate with inclination. All commonly employed dust
attenuation curves (such as the Calzetti curve for starbursts, or a power-law
curve) provide poor fits to the ultraviolet colors for moderately and highly
inclined galaxies. This conclusion rests on the fact that the average FUV-NUV
color varies little from face-on to edge-on galaxies, while other colors such
as NUV-u and u-r vary strongly with inclination. After considering a number of
model variations, we are led to speculate that the presence of the strong dust
extinction feature at 2175A seen in the Milky Way (MW) extinction curve is
responsible for the observed trends. Independent of our interpretation, these
results imply that the modeling of dust attenuation in the ultraviolet is
significantly more complicated than traditionally assumed. These results also
imply a very weak dependence of the FUV-NUV color on total FUV attenuation, and
we conclude from this that it is extremely difficult to use only the observed
UV spectral slope to infer the total UV dust attenuation, as is commonly done.
We propose several simple tests that might finally identify the grain
population responsible for the 2175A feature.Comment: 16 pages, 10 figures. ApJ accepte
ChAInGeS: The Chandra Arp Interacting Galaxies Survey
We have conducted a statistical analysis of the ultra-luminous X-ray point
sources (ULXs; L(X) >= 10^39 erg/s) in a sample of galaxies selected from the
Arp Atlas of Peculiar Galaxies. We find a possible enhancement of a factor of
~2-4 in the number of ULXs per blue luminosity for the strongly interacting
subset. Such an enhancement would be expected if ULX production is related to
star formation, as interacting galaxies tend to have enhanced star formation
rates on average. For most of the Arp galaxies in our sample, the total number
of ULXs compared to the far-infrared luminosity is consistent with values found
earlier for spiral galaxies. This suggests that for these galaxies, ULXs trace
recent star formation. However, for the most infrared-luminous galaxies, we
find a deficiency of ULXs compared to the infrared luminosity. For these very
infrared-luminous galaxies, AGNs may contribute to powering the far-infrared;
alternatively, ULXs may be highly obscured in the X-ray in these galaxies and
therefore not detected by these Chandra observations. We determined local
UV/optical colors within the galaxies in the vicinity of the candidate ULXs
using GALEX UV and SDSS optical images. In most cases, the distributions of
colors are similar to the global colors of interacting galaxies. However, the u
- g and r - i colors at the ULX locations tend to be bluer on average than
these global colors, suggesting that ULXs are preferentially found in regions
with young stellar populations. In the Arp sample there is a possible
enhancement of a factor of ~2 - 5 in the fraction of galactic nuclei that are
X-ray bright compared to more normal spirals.Comment: 28 pages, 7 figures, Astronomical Journal, in pres
The Neutral Hydrogen Properties of Galaxies in Gas-rich Groups
We present an analysis of the integrated neutral hydrogen (Hi) properties for 27 galaxies within nine low mass, gas-rich, late-type dominated groups which we denote \Choirs". We find that majority of the central Choir galaxies have average Hi content: they have a normal gas-mass fraction with respect to isolated galaxies of the same stellar mass. In contrast, we find more satellite galaxies with a lower gas-mass fraction than isolated galaxies of the same stellar mass. A likely reason for the lower gas content in these galaxies is tidal stripping. Both the specific star formation rate and the star formation efficiency of the central group galaxies are similar to galaxies in isolation. The Choir satellite galaxies have similar specific star formation rate as galaxies in isolation, therefore satellites that exhibit a higher star formation efficiency simply owe it to their lower gas-mass fractions. We find that the most Hi massive galaxies have the largest Hi discs and fall neatly onto the Hi size-mass relation, while outliers are galaxies that are experiencing interactions. We find that high specific angular momentum could be a reason for galaxies to retain the large fraction of Hi gas in their discs. This shows that for the Choir groups with no evidence of interactions, as well as those with traces of minor mergers, the internal galaxy properties dominate over the effects of residing in a group. The probed galaxy properties strengthen evidence that the Choir groups represent the early stages of group assembly
The Small Isolated Gas Rich Irregular Dwarf (SIGRID) Galaxy Sample: Description and First Results
Using an optically-unbiased selection process based on the HIPASS neutral
hydrogen survey, we have selected a sample of 83 spatially isolated, gas-rich
dwarf galaxies in the southern hemisphere with cz between 350 and 1650 km s-1,
and with R-band luminosities and HI masses less than that of the Small
Magellanic Cloud. The sample is an important population of dwarf galaxies in
the local Universe, all with ongoing star formation, and most of which have no
existing spectroscopic data. We are measuring the chemical abundances of these
galaxies, using the Integral Field Spectrograph on the ANU 2.3m telescope, the
Wide Field Spectrograph (WiFeS). This paper describes our survey criteria and
procedures, lists the survey sample, and reports on initial observations.Comment: 13 figures, 3 table. Accepted for publication in The Astronomical
Journa
Safety and feasibility of switching from phenytoin to levetiracetam monotherapy for glioma-related seizure control following craniotomy: a randomized phase II pilot study
Seizures are common in patients with gliomas, and phenytoin (PHT) is frequently used to control tumor-related seizures. PHT, however, has many undesirable side effects (SEs) and drug interactions with glioma chemotherapy. Levetiracetam (LEV) is a newer antiepileptic drug (AED) with fewer SEs and essentially no drug interactions. We performed a pilot study testing the safety and feasibility of switching patients from PHT to LEV monotherapy for postoperative control of glioma-related seizures. Over a 13-month period, 29 patients were randomized in a 2:1 ratio to initiate LEV therapy within 24 h of surgery or to continue PHT therapy. 6 month follow-up data were available for 15 patients taking LEV and for 8 patients taking PHT. In the LEV group, 13 patients (87%) were seizure-free. In the PHT group, 6 patients (75%) were seizure-free. Reported SEs at 6 months was as follows (%LEV/%PHT group): dizziness (0/14), difficulty with coordination (0/29), depression (7/14) lack of energy or strength (20/43), insomnia (40/43), mood instability (7/0). The pilot data presented here suggest that it is safe to switch patients from PHT to LEV monotherapy following craniotomy for supratentorial glioma. A large-scale, double-blinded, randomized control trial of LEV versus PHT is required to determine seizure control equivalence and better assess differences in SEs
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