Matt Brorby (U of Iowa) with Philip Kaaret (U of Iowa) Illustration: NASA/CXC/M.Weiss

Transcription

1 Matt Brorby (U of Iowa) with Philip Kaaret (U of Iowa) Illustration: NASA/CXC/M.Weiss

2 Outline Why study ULX vs metallicity? Observations: Einstein, ROSAT, etc: N ULX, L ULX SFR Recent studies: N ULX, L ULX /SFR vs Metallicity Does spectral state depend on metallicity? How could metallicity affect ULX population? Outlook for observable properties of ULX-metallicity effects

3 X-rays in the early Universe Knowing the effects of metallicity on the properties of ULX will lead us to understanding more about the early Universe Recombination z 1000 Dark Ages 20 < z < 1000 Reionization 6 < z < 20 Currently Ionized and warm (IGM)

4 X-rays in the early Universe X-rays have a large mean free path, λ X (cmpc) E X ev (see McQuinn2012; Mesinger+2013; Pacucci+2014) Allows for more uniform ionization Most of X-ray energy is deposited as heat (left over energy after ionization) (Shull & van Steenberg 1985) Would delay the end of reionization due to thermal feedback

5 X-rays in the early Universe (Fialkov, Barkana, & Visbal 2014) Fiducial model of X-ray emission L X SFR = f X [erg s 1 M 1 yr] f X = 1 Reduced X-ray emission f X = 1 10 Enhanced X-ray emission f X = 10 Minimum of curve is beginning of X-ray heating. Above T 21 = 0, reionization begins. (Fialkov, Barkana, & Visbal 2014) Soft XRB spectrum Hard XRB spectrum

6 Gravitational Waves from BH-BH binary LIGO Scientific Collaboration and Virgo Collaboration (2016) Initial black hole masses of M and M Final mass of M The formation of such massive black holes from stellar evolution requires weak massive-star winds, which are possible in stellar environments with metallicity lower than 0.5 Z. Abbott et al. (2016) (LIGO Scientific Collaboration and Virgo Collaboration)

7 Occurrence frequency (%) ULX correlation with star formation rate Number of ULX correlates with star formation Irwin, Bregman, Athey (2004) Liu, Bregman, Irwin (2006) L X > erg/s L X > erg/s Star formation rate (M /yr)

8 ULX prefer dwarf galaxies Walton, Roberts, Mateos, Heard (2011) Tremonti, et al. (2004) Galaxy Mass-Metallicity Relation N ULX per 10 6 M ULX specific frequency increases with decreasing host galaxy mass. Hint of metallicity at play? See also: Swartz, Soria, Tennant (2008)

9 ULX appear to prefer the more metal-poor dwarfs Pakull & Mirioni (2002) Mapelli et al. (2010): N ULX /SFR for sample of non-elliptical galaxies. Prestwich et al. (2013): N ULX for individual SINGS galaxies, intermediate metallicity galaxies and the combined metal poor and extremely metal-poor galaxies (XMPG).

10 Local Proxies to Early Universe Galaxies First galaxies are expected to be small in size and have very low metallicities. Blue compact dwarf galaxy (BCD): Intense, recent star formation (blue) Small ( 1 kpc), irregular galaxy made up of clusters (compact) Low mass (dwarf) dominated by gas mass IMAGE: Hubblesite.org Alessandra Aloisi and Marco Sirianni of STScI BCD: I Zwicky 18

11 Conclusions of BCD Study Brorby, Kaaret, & Prestwich (2014) The XLF normalization for BCDs is enhanced by a factor of 9.7 ± 3.2 compared to near-solar metallicity galaxies Consistent with previous studies (Kaaret et al. 2011; Prestwich et al. 2013, Basu-Zych et al. 2013) Fits in with predictions of X-ray binary formation in the early universe (Mirabel et al. 2011, Fragos et al. 2013) Z Z Z 0.1 Z Mineo et al. (2012) Brorby et al. (2014); Mineo et al. (2012)

12 Local Proxies to Early Universe Galaxies Large, gas-rich galaxies formed after the first dwarf galaxies (hierarchical structure formation) with properties similar to those galaxies observed using the Lyman break technique (Lyman Break Galaxies). Lyman break analogs (LBA) display these qualities as well. (Heckman+2005; Hoopes+2007) Best known local comparison to Lyman break galaxies (LBGs): Physical size, stellar mass, gas velocity dispersion, metallicity, SFR 912 A 1216 A Pettini (2003): Courtesy of Kurt Adelberger Lyman break technique

13 L X of SF Galaxies Brorby, Kaaret, Mirabel, & Prestwich (2016) Evidence for L X SFR Metallicity Plane log L X log SFR BCD (Brorby+2014) Douna+2015 BCD Upper Limit (Brorby+2014) Spiral/Irregulars (Mineo+2012) LBA (Brorby+2016) σ = 0.34 dex 12 + log(ο/h)

14 L X of SF Galaxies Brorby, Kaaret, Mirabel, & Prestwich (2016) Evidence for L X SFR Metallicity Plane BCD (Brorby+2014) Douna+2015 BCD Upper Limit (Brorby+2014) Spiral/Irregulars (Mineo+2012) LBA (Brorby+2016)

15 ULX population and total X-ray luminosity are enhanced at lower metallicities in SF galaxies. Mapelli+2010 Prestwich+2013 Walton+2011

16 Do spectral properties change with metallicity? 71% of flux from sources with L X erg/s in HMXB population Spectral shape of brightest X-ray sources has effect on heating of IGM in the early Universe (Kaaret 2014) Significant curvature in ULX spectra weakens the constraints from the soft X-ray background on the emission from early, bright HMXBs. z = 0 Γ = 2 Γ = 1.5, E c = 6.0 kev Γ = 0.8, E c = 2.1 kev z = 6 Kaaret (2014)

17 Two BCD Galaxies Containing ULX ULX-like vs BHB-like VII Zw 403 X-ray Spectrum (Suzaku) Z = Z I Zw 18 X-ray Spectra (Chandra & XMM-Newton) Z = Z L X = erg/s High, soft state L X = erg/s Hard, ultraluminous state L X = erg/s Low, hard state Brorby et al. (2015) Kaaret & Feng (2013)

18 Holmberg II & IX ULX-like spectra Walton, Middleton, Rana, et al. (2015) Walton, Miller, Harrison, et al. (2013) Straight power law XMM-Newton (pn, MOS) NuSTAR (FPMA, FPMB) Suzaku (FI-XIS, BI-XIS) Holmberg II X-1 Z 0.2 Z (Egorov et al. 2013). Z = 0.1 Z (Morales-Luis et al. 2011) Cutoff power law Holmberg IX X-1 Suzaku Z 0.4 Z (Makarova et al. 2002)

19 The ULX is located inside an association of young stars. Holmberg IX X-1 + Part of a loose cluster Holmberg II X-1 M81 GALEX:GII; NUV; PI:John Huchra The ULX is located in a dense star-forming region of the galaxy which may indicate a dynamically formed IMBH dynamical center Brorby et al. (2015) Ott et al. (2005)

20 Walton, Middleton, Rana, et al. (2015) Holmberg II X-1 Walton, Miller, Harrison, et al. (2013) Holmberg IX X-1 Straight power law XMM-Newton (pn, MOS) NuSTAR (FPMA, FPMB) Suzaku (FI-XIS, BI-XIS) Cutoff power law I Zw 18 X-ray Spectra (Chandra & XMM-Newton) VII Zw 403 X-ray Spectrum (Suzaku) IMBH candidate? Kaaret & Feng (2013) Brorby et al. (2015)

21 Summary of observational studies ULX population and total X-ray luminosity are enhanced at lower metallicities in SF galaxies. ULX observed in the metal-poor galaxies seem to exhibit same spectral behavior as ULX in other galaxies. Studies of ULXs in very low-metallicity environments will help to predict effects of X-ray heating in the early Universe for future radio observations.

22 Ultraluminous X-ray Sources and metallicity How do metallicity effects come into play for each of these situations? Neutron star } Similar to HMXB evolution Stellar mass BH Intermediate mass BH and massive stellar BH Dynamics of young (< 100 Myr), dense ( 10 3 M pc 3 ) star clusters (e.g., Mapelli+2016) Low metallicity -> weak winds -> massive stars + denser cluster core -> more interactions

23 What determines the number of ULXs? Initial Mass Function (IMF) # of High Mass Binaries As an extension of HMXB population Star Formation (SFR) Binary Fraction and Separation Common envelope survivability and stellar wind strength # of ULX Mineo et al. (2012)

24 Luminosity Initial Mass Function (IMF) Makes the Main Sequence Seems to be universal IMF SFR Binary Fraction and Separation # of High Mass Binaries CE Phase and Winds # of ULX Crosby et al. 2013) Temperature

25 Fraction of Star with Companions (%) Initial Binary Fraction Binaries more common for high mass stars in clusters and OB associations Binaries appear to be much more common in high mass stars with the binary fraction approaching 100 percent above a few M. Dependence on metallicity? IMF SFR Binary Fraction and Separation # of High Mass Binaries CE Phase and Winds # of ULX Spectral type Figure from Raghavan et al. (2010). O-type: Mason et al. (1998a, 2009). B-A type: Shatsky & Tokovinin (2002), Kobulnicky & Fryer (2007), Kouwenhoven et al. (2007)

26 More binaries survive common envelope phase at low metallicity IMF SFR Binary Fraction and Separation # of High Mass Binaries CE Phase and Winds # of ULX Dr. Andreas Irrgang: Dr. Karl Remeis-Sternwarte Bamberg Astronomical Institute of the University Erlangen-Nuremberg Van den Heuvel & Heise (1972)

27 More binaries survive common envelope phase at low metallicity Linden+2010 IMF SFR Binary Fraction and Separation # of High Mass Binaries CE Phase and Winds # of ULX Belczynski Thomson/Brooks Cole

28 Low Metallicity -> Weaker winds Stellar winds are driven by resonant lines in metals Lower metallicity results in less effective radiation pressure and thus weaker winds Weaker winds result in less mass loss and larger stars at end of life phase -> massive compact objects Wind momentum Luminosity relation (WLR) Decreasing metallicity Mokiem+2007

29 Compact object mass vs progenitor mass vs metallicity Mapelli, Zampieri, Ripamonti, & Bressan (2013) Fryer, Belczynski, Wiktorowicz, et al. (2012) Zampieri & Roberts (2009)

30 Compact object mass vs progenitor mass vs metallicity Gravitational wave sources Fryer, Belczynski, Wiktorowicz, et al. (2012) Abbott et al. (2016) (LIGO Scientific Collaboration and Virgo Collaboration)

31 Linden+2010 * Binary fraction distribution * Binary separation distribution Z = Z Z = 0.1 Z IMF # of High Mass Binaries * Decreasing metallicity SFR Binary Fraction and Separation CE Phase and Winds # of ULX Mineo et al. (2012); Mineo et Brorby al. (2012) et al. (2014)

32 Population Synthesis of binaries Below 20% solar metallicity, population synthesis models show rapid increase in X-ray luminosity per SFR for bright HMXBs (ULX). (See Mapelli+2011; Belcynski+2010 for alternative simulations) 20% solar Fragos+(2013) Brorby et al. (2016) Linden+2010 Prestwich et al. (2013)

33 Summary ULX populations are enhanced at low metallicities. Simulations suggest more massive, close binaries (are ULX short orbital period binaries?) ULX spectra have no known dependence on metallicity. Simulations agree with observations of metallicity dependence due to weaker stellar winds, survivability of CE phase, dynamical interactions.

34 Possible pursuits (talks later this week might tell us more about this) Improved sampling of ULX properties across metallicity Shorter period ULX (hours, days) -> close binary, RLO (increases at low-z) Measurements of M BH in low metallicity environments Age and density of star forming region is important for dynamical interactions vs stellar evolution More accurate metallicity measurements X-ray/optical lines from immediate region around ULX may also give hints about formation Enhanced metallicity -> SN Unchanged metallicity -> Direct collapse

35 THANK YOU