arXiv subjects

D. R. Weisz

Publications and source records attributed to D. R. Weisz.

At least 19 recordsLinked to original sources

arXiv2025

Discovery of SiC and Iron Dust Around AGB Stars in the very Metal-Poor Sextans A Dwarf Galaxy with JWST: Implications for Dust Production at High Redshift

Low-resolution infrared spectroscopy from JWST confirms the presence of SiC and likely metallic iron dust around asymptotic giant branch (AGB) stars in the Sextans A dwarf galaxy, which has a metallicity ~1%-7% Z_sun. While metal-poor carbon-rich AGB stars are known to produce copious amounts of amorphous carbon dust owing to the dredge up of newly synthesized carbon, this is the first time that Si- and Fe-bearing dust has been detected at this extreme metallicity. Of the six AGB stars observed, one is an intermediate-mass (~1.2-4 M_sun) carbon star showing SiC dust, and another is an oxygen-rich M-type star with mass ~4-5 M_sun that is likely undergoing hot bottom burning. The infrared excess of the M-type star is strong, but featureless. We tested multiple dust species, and find that it is best fit with metallic iron dust. Assuming its dust-production rate stays constant over the final 2-3x10^4 yr of its evolution, this star will produce ~0.9-3.7 times the iron dust mass predicted by models, with the range depending on the adopted stellar mass. The implications for dust production in high-redshift galaxies are potentially significant, especially regarding the assumed dust species used in dust evolution models and the timescale of AGB dust formation. Stars on the upper end of the AGB mass range can begin producing dust as early as 30-50 Myr after they form, and they may therefore rival dust production by supernovae at high redshift.

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arXiv2025

The Hubble Space Telescope Survey of M31 Satellite Galaxies IV. Survey Overview and Lifetime Star Formation Histories

From $>1000$ orbits of HST imaging, we present deep homogeneous resolved star color-magnitude diagrams that reach the oldest main sequence turnoff and uniformly measured star formation histories (SFHs) of 36 dwarf galaxies ($-6 \ge M_V \ge -17$) associated with the M31 halo, and for 10 additional fields in M31, M33, and the Giant Stellar Stream. From our SFHs we find: i) the median stellar age and quenching epoch of M31 satellites correlate with galaxy luminosity and galactocentric distance. Satellite luminosity and present-day distance from M31 predict the satellite quenching epoch to within $1.8$ Gyr at all epochs. This tight relationship highlights the fundamental connection between satellite halo mass, environmental history, and star formation duration. ii) There is no difference between the median SFH of galaxies on and off the great plane of Andromeda satellites. iii) $\sim50$\% of our M31 satellites show prominent ancient star formation ($>12$ Gyr ago) followed by delayed quenching ($8-10$ Gyr ago), which is not commonly observed among the MW satellites. iv) A comparison with TNG50 and FIRE-2 simulated satellite dwarfs around M31-like hosts show that some of these trends (dependence of SFH on satellite luminosity) are reproduced in the simulations while others (dependence of SFH on galactocentric distance, presence of the delayed-quenching population) are weaker or absent. We provide all photometric catalogs and SFHs as High-Level Science Products on MAST.

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arXiv2024

The JWST Resolved Stellar Populations Early Release Science Program VII. Stress Testing the NIRCam Exposure Time Calculator

We empirically assess estimates from v3.0 of the JWST NIRCam Exposure Time Calculator (ETC) using observations of resolved stars in Local Group targets taken as part of the Resolved Stellar Populations Early Release Science (ERS) Program. For bright stars, we find that: (i) purely Poissonian estimates of the signal-to-noise ratio (SNR) are in good agreement between the ETC and observations, but non-ideal effects (e.g., flat field uncertainties) are the current limiting factor in the photometric precision that can be achieved; (ii) source position offsets, relative to the detector pixels, have a large impact on the ETC saturation predictions and introducing sub-pixel dithers in the observation design can improve the saturation limits by up to ~1 mag. For faint stars, for which the sky dominates the error budget, we find that the choice in ETC extraction strategy (e.g., aperture size relative to point spread function size) can affect the exposure time estimates by up to a factor of 5. We provide guidelines for configuring the ETC aperture photometry to produce SNR predictions in line with the ERS data. Finally, we quantify the effects of crowding on the SNRs over a large dynamic range in stellar density and provide guidelines for approximating the effects of crowding on SNRs predicted by the ETC.

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arXiv2023

The Hubble Space Telescope Survey of M31 Satellite Galaxies II. The Star Formation Histories of Ultra-Faint Dwarf Galaxies

We present the lifetime star formation histories (SFHs) for six ultra-faint dwarf (UFD; $M_V>-7.0$, $ 4.9<\log_{10}({M_*(z=0)}/{M_{\odot}})<5.5$) satellite galaxies of M31 based on deep color-magnitude diagrams constructed from \textit{Hubble Space Telescope} imaging. These are the first SFHs obtained from the oldest main sequence turn-off of UFDs outside the halo of the Milky Way (MW). We find that five UFDs formed at least 50\% of their stellar mass by $z=5$ (12.6~Gyr ago), similar to known UFDs around the MW, but that 10-40\% of their stellar mass formed at later times. We uncover one remarkable UFD, \A{XIII}, which formed only 10\% of its stellar mass by $z=5$, and 75\% in a rapid burst at $z\sim2-3$, a result that is robust to choices of underlying stellar model and is consistent with its predominantly red horizontal branch. This "young" UFD is the first of its kind and indicates that not all UFDs are necessarily quenched by reionization, which is consistent with predictions from several cosmological simulations of faint dwarf galaxies. SFHs of the combined MW and M31 samples suggest reionization did not homogeneously quench UFDs. We find that the least massive MW UFDs ($M_*(z=5) \lesssim 5\times10^4 M_{\odot}$) are likely quenched by reionization, whereas more massive M31 UFDs ($M_*(z=5) \gtrsim 10^5 M_{\odot}$) may only have their star formation suppressed by reionization and quench at a later time. We discuss these findings in the context of the evolution and quenching of UFDs.

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arXiv2021

Hubble Space Telescope Imaging of Isolated Local Volume Dwarfs GALFA-Dw3 and Dw4

We present observations of the dwarf galaxies GALFA Dw3 and GALFA Dw4 with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). These galaxies were initially discovered as optical counterparts to compact HI clouds in the GALFA survey. Both objects resolve into stellar populations which display an old red giant branch, younger helium burning, and massive main sequence stars. We use the tip of the red giant branch method to determine the distance to each galaxy, finding distances of 7.61$_{-0.29}^{+0.28}$ Mpc and 3.10$_{-0.17}^{+0.16}$ Mpc, respectively. With these distances we show that both galaxies are extremely isolated, with no other confirmed objects within ~1.5 Mpc of either dwarf. GALFA Dw4 is also found to be unusually compact for a galaxy of its luminosity. GALFA Dw3 and Dw4 contain HII regions with young star clusters and an overall irregular morphology; they show evidence of ongoing star formation through both ultraviolet and H$α$ observations and are therefore classified as dwarf irregulars (dIrrs). The star formation histories of these two dwarfs show distinct differences: Dw3 shows signs of a recently ceased episode of active star formation across the entire dwarf, while Dw4 shows some evidence for current star formation in spatially limited HII regions. Compact HI sources offer a promising method for identifying isolated field dwarfs in the Local Volume, including GALFA Dw3 & Dw4, with the potential to shed light on the driving mechanisms of dwarf galaxy formation and evolution.

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arXiv2019

Hubble Space Telescope Imaging of Antlia B: Star Formation History and a New Tip of the Red Giant Branch Distance

A census of the satellite population around dwarf galaxy primary hosts in environments outside the Local Group is essential to understanding $Λ$CDM galaxy formation and evolution on the smallest scales. We present deep optical Hubble Space Telescope imaging of the gas-rich, faint dwarf galaxy Antlia B ($M_V = -9.4$) -- a likely satellite of NGC 3109 ($D = 1.3$ Mpc) -- discovered as part of our ongoing survey of primary host galaxies similar to the Magellanic Clouds. We derive a new tip of the red giant branch (TRGB) distance of $D = 1.35 \pm 0.06$ Mpc ($m-M = 25.65 \pm 0.10$), consistent with membership in the nearby NGC 3109 dwarf association. The color-magnitude diagram shows both a prominent old, metal-poor stellar component and confirms a small population of young, blue stars with ages $\lesssim 1$ Gyr. We use the color-magnitude diagram fitting algorithm MATCH to derive the star formation history and find that it is consistent with the typical dwarf irregular or transitional dwarf galaxy (dTrans) in the Local Group. Antlia B shows relatively constant stellar mass growth for the first $\sim 10-11$ Gyr and almost no growth in the last $\sim 2-3$ Gyr. Despite being gas-rich, Antlia B shows no evidence of active star formation (i.e., no H$α$ emission) and should therefore be classified as a dTrans dwarf. Both Antlia B and the Antlia dwarf (dTrans) are likely satellites of NGC 3109 suggesting that the cessation of ongoing star formation in these galaxies may be environmentally driven. Future work studying the gas kinematics and distribution in Antlia B will explore this scenario in greater detail. Our work highlights the fact that detailed studies of nearby dwarf galaxies in a variety of environments may continue to shed light on the processes that drive the star formation history and evolution of dwarf galaxies more generally.

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arXiv2019

A Dramatic Decrease in Carbon Star Formation in M31

We analyze resolved stellar near-infrared photometry of 21 HST fields in M31 to constrain the impact of metallicity on the formation of carbon stars. Observations of nearby galaxies show that the carbon stars are increasingly rare at higher metallicity. Models indicate that carbon star formation efficiency drops due to the decrease in dredge-up efficiency in metal-rich thermally-pulsing Asymptotic Giant Branch (TP-AGB) stars, coupled to a higher initial abundance of oxygen. However, while models predict a metallicity ceiling above which carbon stars cannot form, previous observations have not yet pinpointed this limit. Our new observations reliably separate carbon stars from M-type TP-AGB stars across 2.6-13.7 kpc of M31's metal-rich disk using HST WFC3/IR medium-band filters. We find that the ratio of C to M stars (C/M) decreases more rapidly than extrapolations of observations in more metal-poor galaxies, resulting in a C/M that is too low by more than a factor of 10 in the innermost fields and indicating a dramatic decline in C star formation efficiency at metallicities higher than [M/H] $\approx$ -0.1 dex. The metallicity ceiling remains undetected, but must occur at metallicities higher than what is measured in M31's inner disk ([M/H] $\gtrsim$ +0.06 dex).

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arXiv2019

First stellar spectroscopy in Leo P

We present the first stellar spectroscopy in the low-luminosity (M_V ~-9.3 mag), dwarf galaxy Leo P. Its significantly low oxygen abundance (3% solar) and relative proximity (~1.6 Mpc) make it a unique galaxy to investigate the properties of massive stars with near-primordial compositions akin to those in the early Universe. From our VLT-MUSE spectroscopy we find the first direct evidence for an O-type star in the prominent HII region, providing an important test case to investigate the potential environmental dependence of the upper end of the initial mass function in the dwarf galaxy regime. We classify 14 further sources as massive stars (and 17 more as candidate massive stars), most likely B-type objects. From comparisons with published evolutionary models we argue that the absolute visual magnitudes of massive stars in very metal-poor systems such as Leo P and I Zw 18 may be fainter by ~0.5 mag compared to Galactic stars. We also present spectroscopy of two carbon stars identified previously as candidate asymptotic-giant-branch stars. Two of three further candidate asymptotic-giant-branch stars display CaII absorption, confirming them as cool, evolved stars; we also recover CaII absorption in the stacked data of the next brightest 16 stars in the upper red giant branch. These discoveries will provide targets for future observations to investigate the physical properties of these objects and to calibrate evolutionary models of luminous stars at such low metallicity. The MUSE data also reveal two 100pc-scale ring structures in Halpha emission, with the HII region located on the northern edge of the southern ring. Lastly, we report serendipitous observations of 20 galaxies, with redshifts ranging from z=0.39, to a close pair of star-forming galaxies at z=2.5.

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arXiv2015

The ACS LCID Project: On the origin of dwarf galaxy types: a manifestation of the halo assembly bias?

We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than being only the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from colour-magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be assigned to two basic types: fast dwarfs that started their evolution with a dominant and short star formation event, and slow dwarfs that formed a small fraction of their stars early and have continued forming stars until the present time (or almost). These two different evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal vs dwarf irregular). Slow and fast dwarfs also differ in their inferred past location relative to the Milky Way and/or M31, which hints that slow dwarfs were generally assembled in lower density environments than fast dwarfs. We propose that the distinction between a fast and slow dwarf galaxy reflects primarily the characteristic density of the environment where they form. At a later stage, interaction with a large host galaxy may play a role in the final gas removal and ultimate termination of star formation.

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arXiv2015

The Chandra Local Volume Survey I: The X-ray Point Source Populations of NGC 55, NGC 2403, and NGC 4214

We present comprehensive X-ray point source catalogs of NGC~55, NGC~2403, and NGC~4214 as part of the Chandra Local Volume Survey. The combined archival observations have effective exposure times of 56.5 ks, 190 ks, and 79 ks for NGC~55, NGC~2403, and NGC~4214, respectively. When combined with our published catalogs for NGC 300 and NGC 404, our survey contains 629 X-ray sources total down to a limiting unabsorbed luminosity of $\sim5\times10^{35}$ erg s$^{-1}$ in the 0.35-8 keV band in each of the five galaxies. We present X-ray hardness ratios, spectral analysis, radial source distributions, and an analysis of the temporal variability for the X-ray sources detected at high significance. To constrain the nature of each X-ray source, we carried out cross-correlations with multi-wavelength data sets. We searched overlapping Hubble Space Telescope observations for optical counterparts to our X-ray detections to provide preliminary classifications for each X-ray source as a likely X-ray binary, background AGN, supernova remnant, or foreground star.

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arXiv2015

The Progenitors of the Milky Way Stellar Halo: Big Bricks Favoured over Little Bricks

We present a census of blue horizontal branch (BHB) and blue straggler (BS) stars belonging to dwarf galaxies and globular clusters, and compare these counts to that of the Milky Way stellar halo. We find, in agreement with earlier studies, that the ratio of BS-to-BHB stars in these satellite populations is dependent on stellar mass. Dwarf galaxies show an increasing BS-to-BHB ratio with luminosity. In contrast, globular clusters display the reverse trend, with N_BS/N_BHB (< 1) decreasing with luminosity. The faintest (L < 10^5 L_Sun) dwarfs have similar numbers of BS and BHB stars (N_BS/N_BHB ~ 1), whereas more massive dwarfs tend to be dominated by BS stars (N_BS/N_BHB ~ 2-40). We find that the BS-to-BHB ratio in the stellar halo is relatively high (N_BS/N_BHB ~ 5-6), and thus inconsistent with the low ratios found in both ultra-faint dwarfs and globular clusters. Our results favour more massive dwarfs as the dominant "building blocks" of the stellar halo, in good agreement with current predictions from LambdaCDM models.

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arXiv2013

Is there a metallicity ceiling to form carbon stars? - A novel technique reveals a scarcity of C stars in the inner M31 disk

We use medium-band near-infrared (NIR) Hubble Space Telescope WFC3 photometry with model NIR spectra of Asymptotic Giant Branch (AGB) stars to develop a new tool for efficiently distinguishing carbon-rich (C-type) AGB stars from oxygen-rich (M-type) AGB stars in galaxies at the edge of and outside the Local Group. We present the results of a test of this method on a region of the inner disk of M31, where we find a surprising lack of C stars, contrary to the findings of previous C star searches in other regions of M31. We find only 1 candidate C star (plus up to 6 additional, less certain C stars candidates), resulting in an extremely low ratio of C to M stars (C/M = (3.3(+20,-0.1))x10^-4) that is 1-2 orders of magnitude lower than other C/M estimates in M31. The low C/M ratio is likely due to the high metallicity in this region which impedes stars from achieving C/O > 1 in their atmospheres. These observations provide stringent constraints evolutionary models of metal-rich AGB stars and suggest that there is a metallicity threshold above which M stars are unable to make the transition to C stars, dramatically affecting AGB mass loss and dust production and, consequently, the observed global properties of metal-rich galaxies.

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arXiv2013

The Snapshot Hubble U-Band Cluster Survey (SHUCS). I. Survey Description and First Application to the Mixed Star Cluster Population of NGC 4041

We present the Snapshot Hubble U-band Cluster Survey (SHUCS), a project aimed at characterizing the star cluster populations of ten nearby galaxies (d<23 Mpc, half within 12 Mpc) through new F336W (U band equivalent) imaging from WFC3, and archival BVI-equivalent data with HST. Completing the UBVI baseline reduces the age-extinction degeneracy of optical colours, thus enabling the measurement of reliable ages and masses for the thousands of clusters covered by our survey. The sample consists chiefly of face-on spiral galaxies at low inclination, in various degrees of isolation (isolated, in group, merging), and includes two AGN hosts. This first paper outlines the survey itself, the observational datasets, the analysis methods, and presents a proof-of-concept study of the large-scale properties and star cluster population of NGC 4041, a massive SAbc galaxy at a distance of 23 Mpc, and part of a small grouping of six giant members. We resolve two structural components with distinct stellar populations, a morphology more akin to merging and interacting systems. We also find strong evidence of a truncated, Schechter-type mass function, and a similarly segmented luminosity function. These results indicate that binning must erase much of the substructure present in the mass and luminosity functions, and might account for the conflicting reports on the intrinsic shape of these functions in the literature. We also note a tidal feature in the outskirts of the galaxy in GALEX UV imaging, and follow it up with a comprehensive multi-wavelength study of NGC 4041 and its parent group. We deduce a minor merger as a likely cause of its segmented structure and the observed pattern of a radially decreasing star formation rate. We propose that combining the study of star cluster populations with broad-band metrics is not only advantageous, but often easily achievable through archival datasets.

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arXiv2012

The Chandra Local Volume Survey: The X-ray Point Source Population of NGC 404

We present a comprehensive X-ray point source catalog of NGC 404 obtained as part of the Chandra Local Volume Survey. A new, 97 ks Chandra ACIS-S observation of NGC 404 was combined with archival observations for a total exposure of ~123 ks. Our survey yields 74 highly significant X-ray point sources and is sensitive to a limiting unabsorbed luminosity of ~6x10^35 erg s^-1 in the 0.35-8 keV band. To constrain the nature of each X-ray source, cross-correlations with multi-wavelength data were generated. We searched overlapping HST observations for optical counterparts to our X-ray detections, but find only two X-ray sources with candidate optical counterparts. We find 21 likely low mass X-ray binaries (LMXBs), although this number is a lower limit due to the difficulties in separating LMXBs from background AGN. The X-ray luminosity functions (XLFs) in both the soft and hard energy bands are presented. The XLFs in the soft band (0.5-2 keV) and the hard band (2-8 keV) have a limiting luminosity at the 90% completeness limit of 10^35 erg s^-1 and 10^36 erg s^-1, respectively, significantly lower than previous X-ray studies of NGC 404. We find the XLFs to be consistent with those of other X-ray populations dominated by LMXBs. However, the number of luminous (>10^37 erg s^-1) X-ray sources per unit stellar mass in NGC 404 is lower than is observed for other galaxies. The relative lack of luminous XRBs may be due to a population of LMXBs with main sequence companions formed during an epoch of elevated star formation ~0.5 Gyr ago.

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arXiv2012

Revealing a Ring-like Cluster Complex in a Tidal Tail of the Starburst Galaxy NGC 2146

We report the discovery of a ring-like cluster complex in the starburst galaxy NGC 2146. The Ruby Ring, so named due to its appearance, shows a clear ring-like distribution of star clusters around a central object. It is located in one of the tidal streams which surround the galaxy. NGC 2146 is part of the Snapshot Hubble U-band Cluster Survey (SHUCS). The WFC3/F336W data has added critical information to the available archival Hubble Space Telescope imaging set of NGC 2146, allowing us to determine ages, masses, and extinctions of the clusters in the Ruby Ring. These properties have then been used to investigate the formation of this extraordinary system. We find evidence of a spatial and temporal correlation between the central cluster and the clusters in the ring. The latter are about 4 Myr younger than the central cluster, which has an age of 7 Myr. This result is supported by the H alpha emission which is strongly coincident with the ring, and weaker at the position of the central cluster. From the derived total H alpha luminosity of the system we constrain the star formation rate density to be quite high, e.g. ~ 0.47 Msun/yr/kpc^2. The Ruby Ring is the product of an intense and localised burst of star formation, similar to the extended cluster complexes observed in M51 and the Antennae, but more impressive because is quite isolated. The central cluster contains only 5 % of the total stellar mass in the clusters that are determined within the complex. The ring-like morphology, the age spread, and the mass ratio support a triggering formation scenario for this complex. We discuss the formation of the Ruby Ring in a "collect & collapse" framework. The predictions made by this model agree quite well with the estimated bubble radius and expansion velocity produced by the feedback from the central cluster, making the Ruby Ring an interesting case of triggered star formation.

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arXiv2012

The Panchromatic Hubble Andromeda Treasury

The Panchromatic Hubble Andromeda Treasury (PHAT) is an on-going HST Multicycle Treasury program to image ~1/3 of M31's star forming disk in 6 filters, from the UV to the NIR. The full survey will resolve the galaxy into more than 100 million stars with projected radii from 0-20 kpc over a contiguous 0.5 square degree area in 828 orbits, producing imaging in the F275W and F336W filters with WFC3/UVIS, F475W and F814W with ACS/WFC, and F110W and F160W with WFC3/IR. The resulting wavelength coverage gives excellent constraints on stellar temperature, bolometric luminosity, and extinction for most spectral types. The photometry reaches SNR=4 at F275W=25.1, F336W=24.9, F475W=27.9, F814W=27.1, F110W=25.5, and F160W=24.6 for single pointings in the uncrowded outer disk; however, the optical and NIR data are crowding limited, and the deepest reliable magnitudes are up to 5 magnitudes brighter in the inner bulge. All pointings are dithered and produce Nyquist-sampled images in F475W, F814W, and F160W. We describe the observing strategy, photometry, astrometry, and data products, along with extensive tests of photometric stability, crowding errors, spatially-dependent photometric biases, and telescope pointing control. We report on initial fits to the structure of M31's disk, derived from the density of RGB stars, in a way that is independent of the assumed M/L and is robust to variations in dust extinction. These fits also show that the 10 kpc ring is not just a region of enhanced recent star formation, but is instead a dynamical structure containing a significant overdensity of stars with ages >1 Gyr. (Abridged)

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arXiv2012

Spectroscopic Constraints on the Form of the Stellar Cluster Mass Function

This contribution addresses the question of whether the initial cluster mass function (ICMF) has a fundamental limit (or truncation) at high masses. The shape of the ICMF at high masses can be studied using the most massive young (<10 Myr) clusters, however this has proven difficult due to low-number statistics. In this contribution we use an alternative method based on the luminosities of the brightest clusters, combined with their ages. If a truncation is present, a generic prediction (nearly independent of the cluster disruption law adopted) is that the median age of bright clusters should be younger than that of fainter clusters. In the case of an non-truncated ICMF, the median age should be independent of cluster luminosity. Here, we present optical spectroscopy of twelve young stellar clusters in the face-on spiral galaxy NGC 2997. The spectra are used to estimate the age of each cluster, and the brightness of the clusters is taken from the literature. The observations are compared with the model expectations of Larsen (2009) for various ICMF forms and both mass dependent and mass independent cluster disruption. While there exists some degeneracy between the truncation mass and the amount of mass independent disruption, the observations favour a truncated ICMF. For low or modest amounts of mass independent disruption, a truncation mass of 5-6*10^5 Msun is estimated, consistent with previous determinations. Additionally, we investigate possible truncations in the ICMF in the spiral galaxy M83, the interacting Antennae galaxies, and the collection of spiral and dwarf galaxies present in Larsen (2009) based on photometric catalogues taken from the literature, and find that all catalogues are consistent with having a (environmentally dependent) truncation in the cluster mass functions.

astro-ph.CO↗

arXiv2011

Chandra Detection of SN 2010da Four Months After Outburst: Evidence for a Supergiant X-ray Binary in NGC 300

We present the results of a 63 ks {\it Chandra} observation of the "supernova impostor" SN 2010da four months after it was first observed on 25 May 2010. We detect an X-ray source at $\sim7σ$ confidence coincident with the optical location of the SN 2010da outburst. Our imaging analysis has revealed a hard central point source, surrounded by soft diffuse emission extending as far as $\sim$8\asn north of the central source. The diffuse emission has a hardness ratio, 0.35-2 keV luminosity ($\sim6\times10^{35}$ erg s$^{-1}$), and size ($\sim20$ pc) consistent with that of a supernova remnant, although the low number of counts prohibits detailed spectral modeling. Our best-fit spectral model for the hard central source is a black body ($kT = 1.79^{+0.66}_{-0.43}$ keV) with no evidence for intrinsic absorption beyond the Galactic column. We estimate the 0.3-10 keV luminosity to be 1.7$^{+0.2}_{-0.5}\times10^{37}$ erg s$^{-1}$, a factor of $\sim$25 decrease since the initial outburst four months previously. The high X-ray luminosity and slow fading rate is not consistent with this object being a single massive star undergoing an outburst; instead, we favor the scenario where the massive star powering the SN 2010da optical transient is part of a wind-fed supergiant X-ray binary system with a compact companion powering the observed X-ray emission.

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