A Deep XMM-Newton Survey of M33: Point Source Catalog, Source Detection and Characterization of Overlapping Fields

We have obtained a deep 8-field XMM-Newton mosaic of M33 covering the galaxy out to the D$_{25}$ isophote and beyond to a limiting 0.2--4.5 keV unabsorbed flux of 5$\times$10$^{-16}$ erg cm$^{-2}$ s$^{-1}$ (L${>}$4$\times$10$^{34}$ erg s$^{-1}$ at the distance of M33). These data allow complete coverage of the galaxy with high sensitivity to soft sources such as diffuse hot gas and supernova remnants. Here we describe the methods we used to identify and characterize 1296 point sources in the 8 fields. We compare our resulting source catalog to the literature, note variable sources, construct hardness ratios, classify soft sources, analyze the source density profile, and measure the X-ray luminosity function. As a result of the large effective area of XMM-Newton below 1 keV, the survey contains many new soft X-ray sources. The radial source density profile and X-ray luminosity function for the sources suggests that only $\sim$15% of the 391 bright sources with L${>}$3.6$\times$10$^{35}$ erg s$^{-1}$ are likely to be associated with M33, and more than a third of these are known supernova remnants. The log(N)--log(S) distribution, when corrected for background contamination, is a relatively flat power-law with a differential index of 1.5, which suggests many of the other M33 sources may be high-mass X-ray binaries. Finally, we note the discovery of an interesting new transient X-ray source, which we are unable to classify.Comment: 26 pages, 6 tables, 13 figures, accepted for publication in ApJ

The evolution of galaxies and clusters at high spatial resolution with AXIS

Stellar and black hole feedback heat and disperse surrounding cold gas clouds, launching gas flows off circumnuclear and galactic disks and producing a dynamic interstellar medium. On large scales bordering the cosmic web, feedback drives enriched gas out of galaxies and groups, seeding the intergalactic medium with heavy elements. In this way, feedback shapes galaxy evolution by shutting down star formation and ultimately curtailing the growth of structure after the peak at redshift 2-3. To understand the complex interplay between gravity and feedback, we must resolve both the key physics within galaxies and map the impact of these processes over large scales, out into the cosmic web. The Advanced X-ray Imaging Satellite (AXIS) is a proposed X-ray probe mission for the 2030s with arcsecond spatial resolution, large effective area, and low background. AXIS will untangle the interactions of winds, radiation, jets, and supernovae with the surrounding ISM across the wide range of mass scales and large volumes driving galaxy evolution and trace the establishment of feedback back to the main event at cosmic noon.Comment: 29 pages, 18 figures; this white paper is part of a series commissioned for the AXIS Probe mission concep

Young Black Hole and Neutron Star Systems in the Nearby Star-forming Galaxy M33: The NuSTAR View

Abstract We can learn about the formation and evolution of compact objects, such as neutron stars and black holes (BHs), by studying the X-ray emission from accreting systems in nearby star-forming galaxies. The hard (E &gt; 10 keV) X-ray emission in particular allows strong discrimination among the accretion states and compact object types. We conducted a NuSTAR survey (∼600 ks) of the Local Group spiral galaxy M33 to study the distribution of X-ray binary (XRB) accretors in an actively star-forming environment. We constructed color–intensity and color–color diagrams to infer XRB accretion states. Using these diagrams, we have classified 28 X-ray sources in M33 by comparing their hard X-ray colors to those of known systems. Four sources lie in the parameter space occupied by X-ray pulsars, while 8, 10, and 4 sources lie in the parameter space occupied by BHs in the hard, intermediate, and soft states, respectively. The known ultraluminous X-ray source M33 X-8 is also found to be consistent with that source type. Some sources overlap within the Z/Atoll sources due to the overlap of the two categories of BHs and Z/Atoll sources. In contrast to a similar NuSTAR survey of M31 (with a low-mass XRB-dominant population), the source population in M33 is dominated by high-mass XRBs (HMXBs), allowing the study of a very different population with similar sensitivity due to the galaxy's similar distance. This characterization of a population of HMXB accretion states will provide valuable constraints for theoretical XRB population synthesis studies to their formation and evolution.</jats:p