arXiv subjects

G. Meurer

Publications and source records attributed to G. Meurer.

14 recordsLinked to original sources

arXiv2014

The Structure and Stellar Content of the Outer Disks of Galaxies: A New View from the Pan-STARRS1 Medium Deep Survey

We present the results of an analysis of Pan-STARRS1 Medium Deep Survey multi-band (g,r,i,z,y) images of a sample of 698 low-redshift disk galaxies that span broad ranges in stellar mass, star-formation rate, and bulge/disk ratio. We use population synthesis SED fitting techniques to explore the radial distribution of the light, color, surface mass density, mass/light ratio, and age of the stellar populations. We characterize the structure and stellar content of the galaxy disks out to radii of about twice Petrosian r90, beyond which the halo light becomes significant. We measure normalized radial profiles for sub-samples of galaxies in three bins each of stellar mass and concentration. We also fit radial profiles to each galaxy. The majority of galaxies have down-bending radial surface brightness profiles in the bluer bands with a break radius at roughly r90. However, they typically show single unbroken exponentials in the reddest bands and in the stellar surface mass density. We find that the mass/light ratio and stellar age radial profiles have a characteristic "U-shape". There is a good correlation between the amplitude of the down-bend in the surface brightness profile and the rate of the increase in the M/L ratio in the outer disk. As we move from late- to early-type galaxies, the amplitude of the down-bend and the radial gradient in M/L both decrease. Our results imply a combination of stellar radial migration and suppression of recent star formation can account for the stellar populations of the outer disk.

astro-ph.GA↗

arXiv2013

Resolved photometry of Young Massive Clusters in the starburst galaxy NGC 4214

We present the results of deep high resolution imaging performed with ACS/HRC@HST in the most active region of the nearby starburst galaxy NGC 4214. We resolved the stellar populations of five Young Massive Clusters and their surrounding galactic field. The star formation history of this region is characterized by two main bursts occurred within the last 500 Myr, with the oldest episode spread out across an area larger than that covered by the most recent one. The ages derived for the analysed clusters cover a wide range between 6.4<log(t/yr)<8.1 in agreement with those predicted by recent analyses based on integrated photometry. The comparison between the mass of the young associations and that of the surrounding field population with similar ages indicates a high cluster formation efficiency (Gamma~33%) which decreases when old populations are considered. The mass function of the major assembly has been found to be slightly flatter than the Salpeter (1955) law with a hint of mass segregation. We found no clear signatures of multiple stellar populations in the two young (log(t/yr)<6.8) associations where we were able to resolve their innermost region. The masses and sizes of three clusters indicate that at least one of them could evolve toward a globular cluster-like structure.

astro-ph.GA↗

arXiv2010

Hubble Space Telescope WFC3 Early Release Science: Emission-Line Galaxies from Infrared Grism Observations

We present grism spectra of emission-line galaxies (ELGs) from 0.6-1.6 microns from the Wide Field Camera 3 on the Hubble Space Telescope. These new infrared grism data augment previous optical Advanced Camera for Surveys G800L 0.6-0.95 micron grism data in GOODS-South from the PEARS program, extending the wavelength covereage well past the G800L red cutoff. The ERS grism field was observed at a depth of 2 orbits per grism, yielding spectra of hundreds of faint objects, a subset of which are presented here. ELGs are studied via the Ha, [OIII], and [OII] emission lines detected in the redshift ranges 0.2 2.

astro-ph.CO↗

arXiv2009

An Isolated HII Region near ESO 481-G017

We obtained VLA 21-cm observations of the galaxy ESO 481-G017 to determine the environment and trigger of remote star formation traced by a HII region found 43 kpc from the galaxy (in projection). ESO 481-G017 is an early type spiral galaxy with a HI mass of 1.1*10^9 Msun and a distance of 55 Mpc. The isolated HII region has a H-alpha luminosity of 10^38.1 erg s^-1 and minimal continuum emission suggesting that new stars have formed where little or no stars previously existed. The difference in velocity between the HI disk of ESO 481-G017 (3840-4000 km s^-1) and the isolated HII region (4701 +/- 80 km s^-1) indicates the origin of the HII region may be stars forming in a tidal feature or newly triggered star formation in a very low luminosity companion galaxy. The VLA observations shed light on the nature of this young object.

astro-ph.CO↗

arXiv2009

How do Galaxies Accrete Gas and Form Stars?

Great strides have been made in the last two decades in determining how galaxies evolve from their initial dark matter seeds to the complex structures we observe at z=0. The role of mergers has been documented through both observations and simulations, numerous satellites that may represent these initial dark matter seeds have been discovered in the Local Group, high redshift galaxies have been revealed with monstrous star formation rates, and the gaseous cosmic web has been mapped through absorption line experiments. Despite these efforts, the dark matter simulations that include baryons are still unable to accurately reproduce galaxies. One of the major problems is our incomplete understanding of how a galaxy accretes its baryons and subsequently forms stars. Galaxy formation simulations have been unable to accurately represent the required gas physics on cosmological timescales, and observations have only just begun to detect the star formation fuel over a range of redshifts and environments. How galaxies obtain gas and subsequently form stars is a major unsolved, yet tractable problem in contemporary extragalactic astrophysics. In this paper we outline how progress can be made in this area in the next decade.

astro-ph.CO↗

arXiv2008

Far-Ultraviolet Observations of Starburst Galaxies with FUSE: Galactic Feedback in the Local Universe

We have analysed FUSE far-UV spectra of a sample of 16 local starbursts. These galaxies span ranges of almost three orders-of-magnitude in star formation rate and over two orders-of-magnitude in stellar mass. We find that the strongest interstellar absorption-lines are generally blueshifted relative to the galaxy systemic velocity by ~50 to 300 km/s, implying the presence of starburst-driven galactic outflows. The outflow velocites increase on-average with the star formation rate and the star formation rate per unit mass. We find that outflowing coronal-phase (T ~ several hundred thousand K) gas detected via the OVI 1032 absorption line in nearly every galaxy. The kinematics of this outflowing gas differs from the lower-ionization material, and agrees with predictions for radiatively cooling gas (most likely created at the interface between the hot outrushing gas traced by X-rays and cool ambient material). Emission from the coronal gas is not generally detected, implying that radiative cooling by this phase is not affecting the dynamics/energetics of the wind. We find that the weaker interstellar absorption lines lie close to the systemic velocity, implying that the outflowing gas has a lower column density than the quiescent gas in the starburst. From direct observation below the Lyman edge and from the small residual intensity at the core of the CII 1036 line, we conclude that the absolute escape fraction of ionizing radiation is small (typically less than a few percent). This sample provides a unique window on the global properties of local starburst galaxies and a useful comparison sample for understanding spectra of high redshift galaxies.

astro-ph↗

arXiv2007

Resolved Stellar Populations Constituting Extended UV Disks (XUV-disks) in Nearby Galaxies

We describe HST imaging of recent star formation complexes located in the extended UV disk (XUV-disk) component of NGC 5236 (M 83), NGC 5055 (M 63), and NGC 2090. Photometry in four FUV--visible bands permits us to constrain the type of resolved stars and effective age of clusters, in addition to extinction. The preliminary results given herein focus on CMD analysis and clustering properties in this unique star-forming environment.

astro-ph↗

arXiv2007

The Sextet Arcs: a Strongly Lensed Lyman Break Galaxy in the ACS Spectroscopic Galaxy Survey towards Abell 1689

We present results of the HST Advanced Camera for Surveys spectroscopic ground-based redshift survey in the field of A1689. We measure 98 redshifts, increasing the number of spectroscopically confirmed objects by sixfold. We present two spectra from this catalog of the Sextet Arcs, images which arise from a strongly-lensed Lyman Break Galaxy (LBG) at a redshift of z=3.038. Gravitational lensing by the cluster magnifies its flux by a factor of ~16 and produces six separate images with a total r-band magnitude of r_625=21.7. The two spectra, each of which represents emission from different regions of the LBG, show H I and interstellar metal absorption lines at the systemic redshift. Significant variations are seen in Ly-alpha profile across a single galaxy, ranging from strong absorption to a combination of emission plus absorption. A spectrum of a third image close to the brightest arc shows Ly-alpha emission at the same redshift as the LBG, arising from either another spatially distinct region of the galaxy, or from a companion galaxy close to the LBG. Taken as a group, the Ly-alpha equivalent width in these three spectra decreases with increasing equivalent width of the strongest interstellar absorption lines. We discuss how these variations can be used to understand the physical conditions in the LBG. Intrinsically, this LBG is faint, ~0.1L*, and forming stars at a modest rate, ~4 solar masses per year. We also detect absorption line systems toward the Sextet Arcs at z=2.873 and z=2.534. The latter system is seen across two of our spectra.

astro-ph↗

arXiv2006

Far-Ultraviolet & X-ray Observations of VV 114: Feedback in a Local Analog to Lyman Break Galaxies

We have analyzed FUSE, XMM, and Chandra observations of VV 114, a local galaxy merger with strong similarities to typical high-redshift Lyman Break Galaxies (LBGs). Diffuse thermal X-ray emission encompassing VV114 has been observed by Chandra and XMM. This region of hot (kT~0.59 keV) gas has an enhanced alpha to iron element ratio relative to solar abundances and follows the same relation as typical starbursts between its properties (luminosity, size, and temperature) and those of the starburst galaxy (star formation rate, dust temperature, galaxy mass). These results are consistent with the X-ray gas having been produced by shocks driven by a galactic superwind. The FUSE observations of VV 114 show strong, broad interstellar absorption lines with a pronounced blueshifted component(similar to what is seen in LBGs). This implies an outflow of material moving at 300-400 km/s relative to VV 114. The properties of the strong OVI absorption line are consistent with radiative cooling at the interface between the hot outrushing gas seen in X-rays and the cooler material seen in the other outflowing ions in the FUSE data. We show that the wind in VV114 has not created a ``tunnel'' that enables more than a small fraction (< few percent) of the ionizing photons from VV114 to escape into the IGM. Taken together, these data provide a more complete physical basis for understanding the outflows that seem to be generic in LBGs. This will lead to improved insight into the role that such outflows play in the evolution of galaxies and the inter-galactic medium.

astro-ph↗

arXiv2005

The Photometric Performance and Calibration of the HST Advanced Camera For Surveys

We present the photometric calibration of the HST Advanced Camera for Surveys (ACS). We give here an overview of the performance and calibration of the 2 CCD cameras, the Wide Field Channel (WFC) and the High Resolution Channel (HRC), and a description of the best techniques for reducing ACS CCD data. On-orbit observations of spectrophotometric standard stars have been used to revise the pre-launch estimate of the instrument response curves to best match predicted and observed count rates. Synthetic photometry has been used to determine zeropoints for all filters in 3 magnitude systems and to derive interstellar extinction values for the ACS photometric systems. Due to the CCD internal scattering of long wavelength photons, the width of the PSF increases significantly in the near-IR and the aperture correction for photometry with near-IR filters depends on the spectral energy distribution of the source. We provide encircled energy curves and a detailed recipe to correct for the latter effect. Transformations between the ACS photometric systems and the UBVRI and WFPC2 systems are presented. In general, two sets of transformations are available: 1 based on the observation of 2 star clusters; the other on synthetic photometry. We discuss the accuracy of these transformations and their sensitivity to details of the spectra being transformed. Initial signs of detector degradation due to the HST radiative environment are already visible. We discuss the impact on the data in terms of dark rate increase, charge transfer inefficiency, and hot pixel population.

astro-ph↗

arXiv2004

Star Formation at z~6: The UDF-Parallel ACS Fields

We report on the i-dropouts detected in two exceptionally deep ACS fields (B_{435}, V_{606}, i_{775}, and z_{850} with 10 sigma limits of 28.8, 29.0, 28.5, and 27.8, respectively) taken in parallel with the UDF NICMOS observations. Using an i-z>1.4 cut, we find 30 i-dropouts over 21 arcmin^2 down to z_AB=28.1, or 1.4 i-dropouts arcmin^{-2}, with significant field-to-field variation (as expected from cosmic variance). This extends i-dropout searches some ~0.9^m further down the luminosity function than was possible in the GOODS field, netting a ~7x increase in surface density. An estimate of the size evolution for UV bright objects is obtained by comparing the composite radial flux profile of the bright i-dropouts (z<27.2) with scaled versions of the HDF-N + HDF-S U-dropouts. The best-fit is found with a (1+z)^{-1.57_{-0.53} ^{+0.50}} scaling in size (for fixed luminosity), extending lower redshift (1<z<5) trends to z~6. Adopting this scaling and the brighter i-dropouts from both GOODS fields, we make incompleteness estimates and construct a z~6 LF in the rest-frame continuum UV (~1350 A) over a 3.5 magnitude baseline, finding a shape consistent with that found at lower redshift. To evaluate the evolution in the LF from z~3.8, we make comparisons against different scalings of a lower redshift B-dropout sample. Though a strong degeneracy is found between luminosity and density evolution, our best-fit model scales as (1+z)^{-2.8} in number and (1+z)^0.1 in luminosity, suggesting a rest-frame continuum UV luminosity density at z~6 which is just 0.38_{-0.07} ^{+0.09}x that at z~3.8. Our inclusion of size evolution makes the present estimate lower than previous z~6 estimates.

astro-ph↗

arXiv2003

Faint Galaxies in deep ACS observations

We present the analysis of the faint galaxy population in the Advanced Camera for Surveys (ACS) Early Release Observation fields VV 29 (UGC 10214) and NGC 4676. Here we attempt to thoroughly consider all aspects relevant for faint galaxy counting and photometry, developing methods which are based on public software and that are easily reproducible by other astronomers. Using simulations we determine the best SExtractor parameters for the detection of faint galaxies in deep HST observations, paying special attention to the issue of deblending, which significantly affects the normalization and shape of the number count distribution. We confirm, as claimed by Bernstein, Freedman and Madore (2002), that Kron-like magnitudes, such as the ones generated by SExtractor, can miss more than half of the light of faint galaxies, what dramatically affects the slope of the number counts. We present catalogs for the VV 29 and NGC 4676 fields with photometry in the g,V and I bands. We also show that combining the bayesian software BPZ with superb ACS data and new spectral templates enables us to estimate reliable photometric redshifts for a significant fraction of galaxies with as few as three filters. After correcting for selection effects, we measure slopes of 0.32+- 0.01 for 22 < g < 28, 0.34+-0.01 for 22< V <27.5 and 0.33+-0.01 for 22 < I < 27. The counts do not flatten (except perhaps in the g-band), up to the depth of our observations. We find that the faint counts m_{AB}> 25.5 can be well approximated in all our filters by a passive luminosity evolution model based on the COMBO-17 luminosity function (α=-1.5), with a strong merging rate following the prescription of Glazebrook et al. (1994), ϕ^*\propto (1+Qz), with Q=4.

astro-ph↗

arXiv2001

On the Escape of Ionizing Radiation from Starbursts

Far-ultraviolet spectra obtained with $FUSE$ show that the strong $CIIλ$1036 interstellar absorption-line is essentially black in five of the UV-brightest local starburst galaxies. Since the opacity of the neutral ISM below the Lyman-edge will be significantly larger than in the $CII$ line, these data provide strong constraints on the escape of ionizing radiation from these starbursts. Interpreted as a a uniform absorbing slab, the implied optical depth at the Lyman edge is huge ($τ_0 \geq 10^2$). Alternatively, the areal covering factor of opaque material is typically $\geq$ 94%. Thus, the fraction of ionizing stellar photons that escape the ISM of each galaxy is small: our conservative estimates typically yield $f_{esc} \leq 6%$. Inclusion of extinction due to dust will further decrease $f_{esc}$. An analogous analysis of the rest-UV spectrum of the star-forming galaxy $MS 1512-CB58$ at $z$ =2.7 leads to similar constraints on $f_{esc}$. These new results agree with the constraints provided by direct observations below the Lyman edge in a few other local starbursts. However, they differ from the recently reported properties of star-forming galaxies at $z \geq$ 3. We assess the idea that the strong galactic winds seen in many powerful starbursts clear channels through their neutral ISM. We show empirically that such outflows may be a necessary - but not sufficient - part of the process for creating a relatively porous ISM. We note that observations will soon document the cosmic evolution in the contribution of star-forming galaxies to the metagalactic ionizing background, with important implications for the evolution of the IGM.

astro-ph↗

arXiv1997

Dust and Recent Star Formation in the Core of NGC5253

(Abridged) Ultraviolet and optical narrow and broad band images of NGC5253 obtained with the HST WFPC2 are used to derive the properties of the dust distribution and the recent star formation history of this metal-poor dwarf galaxy. Corrections for the effects of dust are important in the center of NGC5253: dust reddening is markedly inhomogeneous across the galaxy's central 20" region. One of the most obscured regions coincides with the region of highest star formation activity in the galaxy: clouds of more than 9~magnitudes of optical depth at V enshroud a young (2.5~Myr old) stellar cluster in the region. Star formation has been active at least over the past 100 Myr in the core of the galaxy, as indicated by the age distribution of both the blue diffuse stellar population and the bright stellar clusters. The star formation is currently concentrated in a 6" region, about 5 Myr old and with a star formation intensity 10-100 times higher than the average within the central 20". The 2.5 Myr old cluster coincides with the peak intensity of the star formation; its mass may be as large as 10^6 solar masses, making this one a Super-Star-Cluster candidate.

astro-ph↗