Mining for normal galaxies in the First XMM-Newton Serendipitous Source Catalog

This paper uses the 1st XMM Serendipitous Source Catalog compiled by the XMM Science Center to identify low-z X-ray selected normal galaxy candidates. Our sample covers a total area of ~6deg^2 to the 0.5-2keV limit 1e-15cgs. A total of 23 sources are selected on the basis of low X-ray-to-optical flux ratio logfx/fopt<-2, soft X-ray spectral properties and optical spectra, when available, consistent with stellar than AGN processes. This sample is combined with similarly selected systems from the Needles in the Haystack Survey (Georgantopoulos et al. 2005) to provide a total of 46 z<0.2 X-ray detected normal galaxies, the largest low-z sample yet available. This is first used to constrain the normal galaxy logN-logS at bright fluxes (>1e-15cgs). We estimate a slope of -1.46\pm0.13 for the cumulative number counts consistent with the euclidean prediction. We further combine our sample with 23 local (z<0.2) galaxies from the CDF North and South to construct the local X-ray luminosity function of normal galaxies. A Schechter form provides a good fit to the data with a break at logL*~41.02cgs and a slope of -1.76\pm0.10. Finally, for the sample of 46 systems we explore the association between X-ray luminosity and host galaxy properties, such as SFR and stellar mass. We find that the L_X of the emission-line systems correlates with Ha luminosity and 1.4GHz radio power, both providing an estimate of the current star-formation rate. In the case of early type galaxies with absorption line optical spectra we use the K-band as proxy to stellar mass and find a correlation of the form L_X~L_K^1.5. This is flatter than the L_X-L_B relation for local ellipticals. This may be due to either L_K providing a better proxy to galaxy mass or selection effects biasing our sample against very luminous early-type galaxies.Comment: Accepted for publication in MNRA

A multi-wavelength study of Supernova Remnants in six nearby galaxies. I: Detection of new X-ray selected Supernova Remnants with Chandra

We present results from a study of the Supernova Remnant (SNR) population in a sample of six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4449, NGC 4395 and NGC 5204) based on Chandra archival data. We have detected 244 discrete X-ray sources down to a limiting flux of 10^{-15} erg/s. We identify 37 X-ray selected thermal SNRs based on their X-ray colors or spectra, 30 of which are new discoveries. In many cases the X-ray classification is confirmed based on counterparts with SNRs identified in other wavelengths. Three of the galaxies in our sample (NGC 4214, NGC 4395 and NGC 5204) are studied for the first time, resulting in the discovery of 13 thermal SNRs. We discuss the properties (luminosity, temperature, density) of the X-ray detected SNRs in the galaxies of our sample in order to address their dependence on their environment. We find that X-ray selected SNRs in irregular galaxies appear to be more luminous than those in spirals. We attribute this to the lower metalicities and therefore more massive progenitor stars of irregular galaxies or the higher local densities of the ISM. We also discuss the X-ray selected SNR populations in the context of the Star Formation Rate of their host galaxies. A comparison of the numbers of observed luminous X-ray selected SNRs with those expected based on the luminosity functions of X-ray SNRs in the MCs and M33 suggest different luminosity distributions between the SNRs in spiral and irregular galaxies with the latter tending to have flatter distributions.Comment: 56 pages, 14 figures, 26 tables. Accepted for publication in Ap

Deep optical study of the mixed-morphology supernova remnant G 132.7+1.3 (HB3)

We present optical CCD images of the large supernova remnant (SNR) G 132.7+1.3 (HB3) covering its full extent for the first time, in the emission lines of Hα +[N II], [S II], and [O III], where new and known filamentary and diffuse structures are detected. These observations are supplemented by new low-resolution long-slit spectra and higher resolution images in the same emission lines. Both the flux-calibrated images and spectra confirm that the optical emission originates from shock-heated gas since the [S II]/Hα > 0.4. Our findings are also consistent with the recently developed emission-line ratio diagnostics for distinguishing SNRs from H II regions. A multiwavelength comparison among our optical data and relevant observations in radio, X-rays, gamma-rays and CO bands, provided additional evidence on the interaction of HB3 with the surrounding clouds and clarified the borders of the SNR and the adjacent cloud. We discuss the supernova (SN) properties and evolution that led to the current observables of HB3 and we show that the remnant has most likely passed at the pressure driven snowplow phase. The estimated SN energy was found to be (3.7 ± 1.5) × 1051 erg and the current SNR age (5.1 ± 2.1) × 104 yr. We present an alternative scenario according to which the SNR evolved in the wind bubble cavity excavated by the progenitor star and currently is interacting with its density walls. We show that the overall mixed morphology properties of HB3 can be explained if the SN resulted by a Wolf−Rayet progenitor star with mass ∼34 M⊙⁠

Galactic and Extragalactic Samples of Supernova Remnants: How They Are Identified and What They Tell Us

Supernova remnants (SNRs) arise from the interaction between the ejecta of a supernova (SN) explosion and the surrounding circumstellar and interstellar medium. Some SNRs, mostly nearby SNRs, can be studied in great detail. However, to understand SNRs as a whole, large samples of SNRs must be assembled and studied. Here, we describe the radio, optical, and X-ray techniques which have been used to identify and characterize almost 300 Galactic SNRs and more than 1200 extragalactic SNRs. We then discuss which types of SNRs are being found and which are not. We examine the degree to which the luminosity functions, surface-brightness distributions and multi-wavelength comparisons of the samples can be interpreted to determine the class properties of SNRs and describe efforts to establish the type of SN explosion associated with a SNR. We conclude that in order to better understand the class properties of SNRs, it is more important to study (and obtain additional data on) the SNRs in galaxies with extant samples at multiple wavelength bands than it is to obtain samples of SNRs in other galaxiesComment: Final 2016 draft of a chapter in "Handbook of Supernovae" edited by Athem W. Alsabti and Paul Murdin. Final version available at https://doi.org/10.1007/978-3-319-20794-0_90-

Star Formation Relations and CO Spectral Line Energy Distributions across the J-ladder and Redshift

We present FIR [50-300 μm]–CO luminosity relations (i.e., log L_FIR = α log L’_co + β) for the full CO rotational ladder from J = 1-0 up to J = 13-12 for a sample of 62 local (z ≤ 0.1) (Ultra) Luminous Infrared Galaxies (LIRGs; L_(IR[8-1000 μm]) > 10^(11) L ☉) using data from Herschel SPIRE-FTS and ground-based telescopes. We extend our sample to high redshifts (z > 1) by including 35 submillimeter selected dusty star forming galaxies from the literature with robust CO observations, and sufficiently well-sampled FIR/submillimeter spectral energy distributions (SEDs), so that accurate FIR luminosities can be determined. The addition of luminous starbursts at high redshifts enlarge the range of the FIR–CO luminosity relations toward the high-IR-luminosity end, while also significantly increasing the small amount of mid-J/high-J CO line data (J = 5-4 and higher) that was available prior to Herschel. This new data set (both in terms of IR luminosity and J-ladder) reveals linear FIR–CO luminosity relations (i.e., α 1) for J = 1-0 up to J = 5-4, with a nearly constant normalization (β ~ 2). In the simplest physical scenario, this is expected from the (also) linear FIR–(molecular line) relations recently found for the dense gas tracer lines (HCN and CS), as long as the dense gas mass fraction does not vary strongly within our (merger/starburst)-dominated sample. However, from J = 6-5 and up to the J = 13-12 transition, we find an increasingly sublinear slope and higher normalization constant with increasing J. We argue that these are caused by a warm (~100 K) and dense (>10^4 cm^(–3)) gas component whose thermal state is unlikely to be maintained by star-formation-powered far-UV radiation fields (and thus is no longer directly tied to the star formation rate). We suggest that mechanical heating (e.g., supernova-driven turbulence and shocks), and not cosmic rays, is the more likely source of energy for this component. The global CO spectral line energy distributions, which remain highly excited from J = 6-5 up to J = 13-12, are found to be a generic feature of the (U)LIRGs in our sample, and further support the presence of this gas component

An X-Ray-Selected Sample of Candidate Black Holes in Dwarf Galaxies

We present a sample of hard X-ray-selected candidate black holes (BHs) in 19 dwarf galaxies. BH candidates are identified by cross-matching a parent sample of ~44,000 local dwarf galaxies (M* = 3 × 10 9 M☉, z < 0.055) with the Chandra Source Catalog and subsequently analyzing the original X-ray data products for matched sources. Of the 19 dwarf galaxies in our sample, eight have X-ray detections reported here for the first time. We find a total of 43 point-like hard X-ray sources with individual luminosities L2-10 keV ~ 10 37 - 10 40 erg s-1. Hard X-ray luminosities in this range can be attained by stellar-mass X-ray binaries (XRBs) and by massive BHs accreting at low Eddington ratio. We place an upper limit of 53% (10/19) on the fraction of galaxies in our sample hosting a detectable hard X-ray source consistent with the optical nucleus, although the galaxy center is poorly defined in many of our objects. We also find that 42% (8/19) of the galaxies in our sample exhibit statistically significant enhanced hard X-ray emission relative to the expected galaxy-wide contribution from low-mass and high-mass XRBs, based on the [data] star formation rate relation defined by more massive and luminous systems. For the majority of these X-ray-enhanced dwarf galaxies, the excess emission is consistent with (but not necessarily due to) a nuclear X-ray source. Follow-up observations are necessary to distinguish between stellar-mass XRBs and active galactic nuclei powered by more massive BHs. In any case, our results support the notion that X-ray-emitting BHs in low-mass dwarf galaxies may have had an appreciable impact on reionization in the early universe

Optical emission-line Luminosity Function models for populations of Supernova Remnants

We present a basic model for the calculation of the luminosity distribution of supernova remnant populations. We construct theoretical Ha and joint [S II] - Ha luminosity functions for supernova remnants by combining prescriptions from a basic evolution model that provides the shock velocity and radius for SNRs of different age and pre-shock density, with shock excitation models that give the gas emissivity for shocks of different physical parameters. We assume a flat age distribution, and we explore the effect of different pre-shock density distributions or different magnetic parameters. We find very good agreement between the shape of the model Ha and the joint [S II] - Ha luminosity functions and those measured from SNR surveys in nearby galaxies.Comment: 11 pages, Accepted for publication in MNRA