15 research outputs found
Elevated hot gas and high-mass X-ray binary emission in low-metallicity galaxies: implications for nebular ionization and intergalactic medium heating in the early universe
High-energy emission associated with star formation has been proposed as a significant source of interstellar
medium (ISM) ionization in low-metallicity starbursts and an important contributor to the heating of the
intergalactic medium (IGM) in the high-redshift (z 8) universe. Using Chandra observations of a sample of 30
galaxies at D ≈ 200–450 Mpc that have high specific star formation rates of 3–9 Gyr−1 and metallicities near
Z ≈ 0.3Ze, we provide new measurements of the average 0.5–8 keV spectral shape and normalization per unit star
formation rate (SFR). We model the sample-combined X-ray spectrum as a combination of hot gas and high-mass
X-ray binary (HMXB) populations and constrain their relative contributions. We derive scaling relations of
Llog 0.5 8 keV
HMXB
– /SFR = 40.19 ± 0.06 and Llog 0.5 2 keV
gas
– /SFR 39.58 ;0.28
0.17
= -
+ significantly elevated compared to local
relations. The HMXB scaling is also somewhat higher than L0.5 8 keV
HMXB
– –SFR-Z relations presented in the literature,
potentially due to our galaxies having relatively low HMXB obscuration and young and X-ray luminous stellar
populations. The elevation of the hot gas scaling relation is at the level expected for diminished attenuation due to a
reduction of metals; however, we cannot conclude that an L0.5 2 keV
gas
– –SFR-Z relation is driven solely by changes in
ISM metal content. Finally, we present SFR-scaled spectral models (both emergent and intrinsic) that span the
X-ray-to-IR band, providing new benchmarks for studies of the impact of ISM ionization and IGM heating in the
early universe
The Large Deficit of HMXB Emission from Luminous Infrared Galaxies: the Case of the Circumnuclear Starburst Ring in NGC 7552
Luminous infrared galaxies (LIRGs), the most extreme star-forming galaxies in
the nearby (D30 Mpc) Universe, show a notable X-ray emission deficiency (up
to a factor of 10) compared with predictions from scaling relations of
galaxy-wide high mass X-ray binary (HMXB) luminosity with star-formation rate.
In the nearby (20 Mpc) LIRG NGC 7552, the majority of the IR emission
originates in a circumnuclear starburst ring, which has been resolved into
several discrete knots of star formation. We present results from recent
Chandra observations of NGC 7552, which reveal significant deficits in the 2-7
keV X-ray luminosities from two of the most powerful star-forming knots. We
hypothesize that the expected luminous HMXB populations in these knots are
either (1) obscured by very large column densities or (2) suppressed due to the
knots having relatively high metallicity and/or very young ages ( 5
Myr). We distinguish between these possibilities using data from recent NuSTAR
observations, whose sensitivity above 10 keV is capable of uncovering heavily
obscured HMXB populations, since emission at these energies is more immune to
absorption effects. We find no evidence of a heavily obscured HMXB population
in the central region of NGC 7552, suggesting suppressed HMXB formation. We
further show that metallicity-dependent scaling relations cannot fully account
for the observed deficit from the most powerful star-forming knots or the
central region as a whole. Thus, we suggest that recent bursts in local star
formation activity likely drive the high within these regions on
timescales 5 Myr, shorter than the timescale required for the
formation of HMXBs.Comment: Accepted for publication in ApJ (17 pages, 3 tables, 8 figures
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 isophote and beyond to a limiting 0.2--4.5 keV unabsorbed
flux of 510 erg cm s (L410
erg s 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 15% of the 391 bright sources with
L3.610 erg s 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 Stellar-age Dependence of X-Ray Emission from Normal Star-forming Galaxies in the GOODS Fields
The Chandra Deep Field-South and North surveys (CDFs) provide unique windows into the cosmic history of X-ray emission from normal (nonactive) galaxies. Scaling relations of normal-galaxy X-ray luminosity (L X) with star formation rate (SFR) and stellar mass (M ∗) have been used to show that the formation rates of low-mass and high-mass X-ray binaries (LMXBs and HMXBs, respectively) evolve with redshift across z ≈ 0-2 following L HMXB/SFR α(1 + z) and L LMXB/M ∗ α(1 + z)2-3. However, these measurements alone do not directly reveal the physical mechanisms behind the redshift evolution of X-ray binaries (XRBs). We derive star formation histories for a sample of 344 normal galaxies in the CDFs, using spectral energy distribution (SED) fitting of FUV-to-FIR photometric data, and construct a self-consistent, age-dependent model of the X-ray emission from the galaxies. Our model quantifies how X-ray emission from hot gas and XRB populations vary as functions of host stellar-population age. We find that (1) the ratio L X/M ∗ declines by a factor of ∼1000 from 0 to 10 Gyr and (2) the X-ray SED becomes harder with increasing age, consistent with a scenario in which the hot gas contribution to the X-ray SED declines quickly for ages above 10 Myr. When dividing our sample into subsets based on metallicity, we find some indication that L X/M ∗ is elevated for low-metallicity galaxies, consistent with recent studies of X-ray scaling relations. However, additional statistical constraints are required to quantify both the age and metallicity dependence of X-ray emission from star-forming galaxies
The Evolution of Galaxies and Clusters at High Spatial Resolution with Advanced X-ray Imaging Satellite (AXIS)
Stellar and black hole feedback heat and disperse surrounding cold gas clouds, launching gas flows off circumnuclear and galactic disks, 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 interstellar medium 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. This white paper is part of a series commissioned for the AXIS Probe mission concept; additional AXIS white papers can be found at the AXIS website