31 research outputs found
Closing the Gap between Observed Low-Mass Galaxy HI Kinematics and CDM Predictions
Testing the standard cosmological model (CDM) at small scales is
challenging. Galaxies that inhabit low-mass dark matter halos provide an ideal
test bed for dark matter models by linking observational properties of galaxies
at small scales (low mass, low velocity) to low-mass dark matter halos.
However, the observed kinematics of these galaxies do not align with the
kinematics of the dark matter halos predicted to host them, obscuring our
understanding of the low-mass end of the galaxy-halo connection. We use deep HI
observations of low-mass galaxies at high spectral resolution in combination
with cosmological simulations of dwarf galaxies to better understand the
connection between dwarf galaxy kinematics and low-mass halos. Specifically, we
use HI line widths to directly compare to the maximum velocities in a dark
matter halo, and find that each deeper measurement approaches the expected
one-to-one relationship between the observed kinematics and the predicted
kinematics in CDM. We also measure baryonic masses and place these on
the Baryonic Tully-Fisher relation (BTFR). Again, our deepest measurements
approach the theoretical predictions for the low-mass end of this relation, a
significant improvement on similar measurements based on line widths measured
at 50\% and 20\% of the peak. Our data also hints at the rollover in the BTFR
predicted by hydrodynamical simulations of CDM for low-mass galaxies.Comment: 13 pages of text, 4 figures, submitted to AAS Journal
A Census of the Extended Neutral Hydrogen around 18 MHONGOOSE Galaxies
We present the analysis of the diffuse, low column density H I environment of 18 MHONGOOSE galaxies. We obtained deep observations with the Robert C. Byrd Green Bank Telescope and reached down to a 3Ï column density detection limit of NHI = 6.3 Ă 1017 cm-2 over a 20 km s-1 line width. We analyze the environment around these galaxies, with a focus on H I gas that reaches column densities below NHI = 1019 cm-2. We calculate the total amount of H I gas in and around the galaxies, revealing that nearly all of these galaxies contained excess H I outside of their disks. We quantify the amount of diffuse gas in the maps of each galaxy, defined by H I gas with column densities below 1019 cm-2, and find a large spread in percentages of diffuse gas. However, by binning the percentage of diffuse H I into quarters, we find that the bin with the largest number of galaxies is the lowest quartile (0%-25% diffuse H I). We identified several galaxies that may be undergoing gas accretion onto the galaxy disk using multiple methods of analysis, including azimuthally averaging column densities beyond the disk, and identifying structure within our integrated intensity (moment 0) maps. We measured H I mass outside the disks of most of our galaxies, with rising cumulative flux even at large radii. We also find a strong correlation between the fraction of diffuse gas in a galaxy and its baryonic mass, and we test this correlation using both Spearman and Pearson correlation coefficients. We see evidence of a dark matter halo mass threshold of Mhalo ⌠1011.1 Mâ in which galaxies with high fractions of diffuse H I all reside below. It is in this regime that cold-mode accretion should dominate. Finally, we suggest a rotation velocity of vrot ⌠80 km s-1 as an upper threshold to find diffuse-gas-dominated galaxies
HuD regulates SOD1 expression during oxidative stress in differentiated neuroblastoma cells and sporadic ALS motor cortex.
The neuronal RNA-binding protein (RBP) HuD plays an important role in brain development, synaptic plasticity and neurodegenerative diseases such as Parkinson's (PD) and Alzheimer's (AD). Bioinformatics analysis of the human SOD1 mRNA 3' untranslated region (3'UTR) demonstrated the presence of HuD binding adenine-uridine (AU)-rich instability-conferring elements (AREs). Using differentiated SH-SY5Y cells along with brain tissues from sporadic amyotrophic lateral sclerosis (sALS) patients, we assessed HuD-dependent regulation of SOD1 mRNA. In vitro binding and mRNA decay assays demonstrate that HuD specifically binds to SOD1 ARE motifs promoting mRNA stabilization. In SH-SY5Y cells, overexpression of full-length HuD increased SOD1 mRNA and protein levels while a dominant negative form of the RBP downregulated its expression. HuD regulation of SOD1 mRNA was also found to be oxidative stress (OS)-dependent, as shown by the increased HuD binding and upregulation of this mRNA after H2O2 exposure. This treatment also induced a shift in alternative polyadenylation (APA) site usage in SOD1 3'UTR, increasing the levels of a long variant bearing HuD binding sites. The requirement of HuD for SOD1 upregulation during oxidative damage was validated using a specific siRNA that downregulated HuD protein levels to 36% and prevented upregulation of SOD1 and 91 additional genes. In the motor cortex from sALS patients, we found increases in SOD1 and HuD mRNAs and proteins, accompanied by greater HuD binding to this mRNA as confirmed by RNA-immunoprecipitation (RIP) assays. Altogether, our results suggest a role of HuD in the post-transcriptional regulation of SOD1 expression during ALS pathogenesis
Detection of the diffuse HI emission in the Circumgalactic Medium of NGC 891 and NGC 4565
We present detections of 21-cm emission from neutral hydrogen (HI) in the
circumgalactic medium (CGM) of the local edge-on galaxies NGC 891 and NGC 4565
using the Robert C. Byrd Green Bank Telescope (GBT). With our 5
sensitivity of cm calculated over a 20 km s
channel, we achieve detections out to kpc along the minor
axes. The velocity width of the CGM emission is as large as that of the disk
km s, indicating the existence of a diffuse component
permeating the halo. We compare our GBT measurements with interferometric data
from the Westerbork Synthesis Radio Telescope (WSRT). The WSRT maps the HI
emission from the disk at high S/N but has limited surface brightness
sensitivity at the angular scales probed with the GBT. After convolving the
WSRT data to the spatial resolution of the GBT (FWHM = 9.1), we find that
the emission detected by the WSRT accounts for %
(%) of the total flux recovered by the GBT from the CGM of NGC
891(NGC 4565). The existence of significant GBT-only flux suggests the presence
of a large amount of diffuse, low column density HI emission in the CGM. For
reasonable assumptions, the extended diffuse HI could account for %
and % of the total HI emission of NGC 891 and NGC 4565.Comment: 14 pages, 5 figures, published in Ap
Detection of diffuse HI emission in the circumgalactic medium of NGC891 and NGC4565 -- II
We probe the neutral circumgalactic medium (CGM) along the major axes of
NGC891 and NGC4565 in 21-cm emission out to kpc using the Green
Bank Telescope (GBT), extending our previous minor axes observations. We
achieve an unprecedented sensitivity of cm
per 20 km s velocity channel. We detect HI with diverse spectral shapes,
velocity widths, and column densities. We compare our detections to the
interferometric maps from the Westerbork Synthesis Radio Telescope (WSRT)
obtained as part of the HALOGAS survey. At small impact parameters,
of the emission detected by the GBT cannot be explained by emission seen in the
WSRT maps, and it increases to at large impact parameters. This
implies the presence of diffuse circumgalactic HI. The mass ratio between HI in
the CGM and HI in the disk is an order of magnitude larger than previous
estimates based on shallow GBT mapping. The diffuse HI along the major axes
pointings is corotating with the HI disk. The velocity along the minor axes
pointings is consistent with an inflow and/or fountain in NGC891 and an
inflow/outflow in NGC4565. Including the circumgalactic HI, the depletion time
and the accretion rate of NGC4565 are sufficient to sustain its star formation.
In NGC891, most of the required accreting material is still missing.Comment: 18 pages, 12 figures, accepted for publication in MNRA
X-ray Properties of NGC 253's Starburst-Driven Outflow
We analyze image and spectral data from 365~ks of observations from
the {\it Chandra} X-ray Observatory of the nearby, edge-on starburst galaxy
NGC~253 to constrain properties of the hot phase of the outflow. We focus our
analysis on the 1.1 to 0.63 kpc region of the outflow and define several
regions for spectral extraction where we determine best-fit temperatures and
metal abundances. We find that the temperatures and electron densities peak in
the central 250 pc region of the outflow and decrease with distance.
These temperature and density profiles are in disagreement with an adiabatic
spherically expanding starburst wind model and suggest the presence of
additional physics such as mass loading and non-spherical outflow geometry. Our
derived temperatures and densities yield few-Myr cooling times in the nuclear
region, which may imply that the hot gas can undergo bulk radiative cooling as
it escapes along the minor axis. Our metal abundances of O, Ne, Mg, Si, S, and
Fe all peak in the central region and decrease with distance along the outflow,
with the exception of Ne which maintains a flat distribution. The metal
abundances indicate significant dilution outside of the starburst region. We
also find estimates on the mass outflow rates which are
in the northern outflow and
in the southern outflow. Additionally, we detect emission from charge exchange
and find it has a significant contribution (\%) to the total broad-band
(~keV) X-ray emission in the central and southern regions of the
outflow.Comment: 15 pages, 9 figure
Molecular Gas Properties on Cloud Scales across the Local Star-forming Galaxy Population
Using the PHANGSâALMA CO(2â1) survey, we characterize molecular gas properties on ~100 pc scales across 102,778 independent sightlines in 70 nearby galaxies. This yields the best synthetic view of molecular gas properties on cloud scales across the local star-forming galaxy population obtained to date. Consistent with previous studies, we observe a wide range of molecular gas surface densities (3.4 dex), velocity dispersions (1.7 dex), and turbulent pressures (6.5 dex) across the galaxies in our sample. Under simplifying assumptions about subresolution gas structure, the inferred virial parameters suggest that the kinetic energy of the molecular gas typically exceeds its self-gravitational binding energy at ~100 pc scales by a modest factor (1.3 on average). We find that the cloud-scale surface density, velocity dispersion, and turbulent pressure (1) increase toward the inner parts of galaxies, (2) are exceptionally high in the centers of barred galaxies (where the gas also appears less gravitationally bound), and (3) are moderately higher in spiral arms than in inter-arm regions. The galaxy-wide averages of these gas properties also correlate with the integrated stellar mass, star formation rate, and offset from the star-forming main sequence of the host galaxies. These correlations persist even when we exclude regions with extraordinary gas properties in galaxy centers, which contribute significantly to the inter-galaxy variations. Our results provide key empirical constraints on the physical link between molecular cloud populations and their galactic environment
Kinematic analysis of the super-extended HI disk of the nearby spiral galaxy M 83
Funding: CE, FB, AB, IB, JdB and JP acknowledge funding from the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation programme (grant agreement No.726384/Empire). TGW acknowledges funding from the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation programme (grant agreement No. 694343). JMDK gratefully acknowledges funding from the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement number 714907). SCOG acknowledges funding from the European Research Council via the ERC Synergy Grant âECOGAL â Understanding our Galactic ecosystem: From the disk of the Milky Way to the formation sites of stars and planetsâ (project ID 855130). WJGdB received funding from the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation programme (grant agreement No 882793 âMeerGasâ).We present new HI observations of the nearby massive spiral galaxy M83, taken with the VLA at 21âł angular resolution (â500 pc) of an extended (1.5 deg2) 10-point mosaic combined with GBT single dish data. We study the super-extended HI disk of M83 (âŒ50 kpc in radius), in particular disc kinematics, rotation and the turbulent nature of the atomic interstellar medium. We define distinct regions in the outer disk (rgal > central optical disk), including ring, southern area, and southern and northern arm. We examine HI gas surface density, velocity dispersion and non-circular motions in the outskirts, which we compare to the inner optical disk. We find an increase of velocity dispersion (Ïv) towards the pronounced HI ring, indicative of more turbulent HI gas. Additionally, we report over a large galactocentric radius range (until rgal ⌠50 kpc) that Ïv is slightly larger than thermal (i.e. > 8 km s-1). We find that a higher star formation rate (as traced by FUV emission) is not always necessarily associated with a higher HI velocity dispersion, suggesting that radial transport could be a dominant driver for the enhanced velocity dispersion. We further find a possible branch that connects the extended HI disk to the dwarf irregular galaxy UGCA365, that deviates from the general direction of the northern arm. Lastly, we compare mass flow rate profiles (based on 2D and 3D tilted ring models) and find evidence for outflowing gas at rgal ⌠2 kpc, inflowing gas at rgal ~ 5.5 kpc and outflowing gas at rgal ~ 14 kpc. We caution that mass flow rates are highly sensitive to the assumed kinematic disk parameters, in particular, to the inclination.Publisher PDFPeer reviewe