arXiv subjects

Margaret Lazzarini

Publications and source records attributed to Margaret Lazzarini.

21 records · Page 2Linked to original sources

arXiv2022

The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) II. The Spatially Resolved Recent Star Formation History of M33

We measure the spatially resolved recent star formation history (SFH) of M33 using optical images taken with the Hubble Space Telescope as part of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. The area covered by the observations used in this analysis covers a de-projected area of $\sim$38 kpc$^{2}$ and extends to $\sim$3.5 and $\sim$2 kpc from the center of M33 along the major and semi-major axes, respectively. We divide the PHATTER optical survey into 2005 regions that measure 24 arcsec, $\sim$100 pc, on a side and fit color magnitude diagrams for each region individually to measure the spatially resolved SFH of M33 within the PHATTER footprint. There are significant fluctuations in the SFH on small spatial scales and also galaxy-wide scales that we measure back to about 630 Myr ago. We observe a more flocculent spiral structure in stellar populations younger than about 80 Myr, while the structure of the older stellar populations is dominated by two spiral arms. We also observe a bar in the center of M33, which dominates at ages older than about 80 Myr. Finally, we find that the mean star formation rate (SFR) over the last 100 Myr within the PHATTER footprint is 0.32$\pm$0.02 M$_{\odot}$ yr$^{-1}$. We measure a current SFR (over the last 10 Myr) of 0.20$\pm$0.03 M$_{\odot}$ yr$^{-1}$. This SFR is slightly higher than previous measurements from broadband estimates, when scaled to account for the fraction of the D25 area covered by the PHATTER survey footprint.

astro-ph.GA↗

arXiv2020

Multiwavelength Characterization of the High Mass X-ray Binary Population of M31

We present our analysis of high quality high mass X-ray binary (HMXB) candidates in M31 selected from point-source optical-counterpart candidates from the Chandra-PHAT survey catalog. We fit the spectral energy distributions (SEDs) of optical counterpart candidates using the Bayesian Extinction and Stellar Tool (BEAST). We used the best-fit luminosity, effective temperature, radius and dust reddening for the companion stars in combination with the local star formation history, dust maps of M31, published X-ray spectral fits from XMM-Newton observations, IR colors, and Chandra X-ray hardness ratios to determine our best sample of HMXB candidates. The age distribution of the HMXB sample appears peaked between 10 and 50 Myr, consistent with findings in other nearby galaxies. Using the age distribution and mean SFR, we find that 80$-$136 HMXBs were produced per unit of star formation rate over the last 50 Myr and 89$-$163 HMXBs were produced per unit of star formation rate over the last 80 Myr, if we expand the assumed age limit beyond the lifetimes of single massive stars. We also calculate the HMXB production rate (HMXBs/M$_{\odot}$) over time, which ranges from $7 \times 10^{-7}$ to $4 \times 10^{-6}$ HMXBs/M$_{\odot}$ over the last 80 Myr, in agreement with both theoretical predictions and measured production rates in other galaxies.

astro-ph.HE↗

arXiv2018

Comparing Chandra and Hubble in the Northern Disk of M31

The X-ray source populations within galaxies are typically difficult to identify and classify from X-ray data alone. We are able to break through this barrier by combining deep new Chandra ACIS-I observations with extensive Hubble Space Telescope imaging from the PHAT survey of the M31 disk. We detect 373 X-ray sources down to 0.35-8.0 keV flux of 10$^{-15}$ erg cm$^{-2}$ s$^{-1}$ over 0.4 square degrees, 170 of which are reported for the first time. We identify optical counterpart candidates for 188 of the 373 sources, after using the HST data to correct the absolute astrometry of our Chandra imaging to 0.1$"$. While 58 of these 188 are associated with point sources potentially in M31, over half (107) of the counterpart candidates are extended background galaxies, 5 are star clusters, 12 are foreground stars, and 6 are supernova remnants. Sources with no clear counterpart candidate are most likely to be undetected background galaxies and low-mass X-ray binaries in M31. The 58 point sources that are not consistent with foreground stars are bright enough that they could be high mass stars in M31; however, all but 8 have optical colors inconsistent with single stars, suggesting that many could be background galaxies or binary counterparts. For point-like counterparts, we examine the star formation history of the surrounding stellar populations to look for a young component that could be associated with a high mass X-ray binary. For the 40 point-like counterpart candidates associated with young populations, we find that their age distribution has two peaks at 15-20 Myr and 40-50 Myr. If we only consider the 8 counterpart candidates with typical high-mass main sequence optical star colors, their age distribution peaks mimic those of the sample of 40. Finally, we find that intrinsic faintness, and not extinction, is the main limitation for finding further counterpart candidates.

astro-ph.GA↗