Matt Brorby (U of Iowa) with Philip Kaaret (U of Iowa)

Illustration: NASA/CXC/M.Weiss http://chandra.harvard.edu/ Outline

• Why study ULX vs metallicity?

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

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

• X-rays have a large mean free path, . � (cMpc) ∝ (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 X-rays in the early Universe (Fialkov, Barkana, & Visbal 2014)

• Fiducial model of X-ray emission • = 3×10� [erg s M yr] ⊙ • � = 1 • Reduced X-ray emission • � = Soft XRB spectrum • Enhanced X-ray emission Hard XRB spectrum

• � = 10 • Minimum of curve is beginning of X- ray heating. (Fialkov, Barkana, & Visbal 2014) • Above � = 0, reionization begins. X-rays in the early Universe (Mirocha 2014) Gravitational Waves from BH-BH binary LIGO Scientific Collaboration and Virgo Collaboration (2016) • Initial black hole masses of 36 M⊙ and 29 M⊙ • Final mass of 62 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 �⊙.” Abbott et al. (2016) (LIGO Scientific Collaboration and Virgo Collaboration) LIGO Collaboration (2016) LIGO Collaboration (2016) Detect Epoch of Reionization and earlier with next gen radio telescopes?

Detectable by eLISA? ULX correlation with star formation rate Number of ULX correlates with star formation

Irwin, Bregman, Athey (2004) Liu, Bregman, Irwin (2006) L > 10 erg/s L > 1.6×10 erg/s Occurrence frequency (%)

Star formation rate (M⊙/yr) ULX prefer dwarf galaxies Tremonti, et al. (2004) Galaxy Mass-Metallicity Relation Walton, Roberts, Mateos, Heard (2011) ⊙ M

0 1 per N

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

ULX specific frequency increases with decreasing host galaxy mass. Hint of metallicity at play? See also: Swartz, Soria, Tennant (2008)

Pakull & Mirioni (2002) ULX appear to prefer the more metal-poor dwarfs Pakull & Mirioni (2002)

Mapelli et al. (2010): N/SFR for sample of Prestwich et al. (2013): N for individual non-ellipticalgalaxies. SINGS galaxies, intermediate metallicity galaxies and the combined metal poor and extremelymetal-poor galaxies(XMPG). 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 Lyman Break Analogs Brorby, Kaaret, Mirabel, & Prestwich (2016) MNRAS, submitted

• Large, gas-rich galaxies formed after the 912 Å 1216 Å first dwarf galaxies (hierarchical structure formation). • These early galaxies would have properties similar to those galaxies observed using the Lyman break technique (Lyman Break Galaxies). • Physical size, stellar mass, gas velocity dispersion, metallicity, SFR • Lyman break analogs (LBAs) display these qualities as well. (Heckman+2005; Hoopes+2007) • Best known local comparison to Lyman break galaxies (LBGs) • Local (� ≤ 0.2) Lyman Break Analogs Brorby, Kaaret, Mirabel, & Prestwich (2016) MNRAS, submitted

• Large, gas-rich galaxies formed after the 912 Å 1216 Å first dwarf galaxies (hierarchical structure formation). • These early galaxies would have properties similar to those galaxies observed using the Lyman break technique (Lyman Break Galaxies). • Physical size, stellar mass, gas velocity dispersion, metallicity, SFR • Lyman break analogs (LBAs) display these qualities as well. (Heckman+2005; Hoopes+2007) • Best known local comparison to Lyman break galaxies (LBGs) • Local (� ≤ 0.2) Conclusions of BCD Study Brorby, Kaaret, & Prestwich (2014)

• The XLF normalization for BCDs is � ∼ �⊙ enhanced by a factor of 9.7 ± 3.2 � ∼ 0.1 �⊙ 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)

Mineo et al. (2012) Brorby et al. (2014); Mineo et al. (2012) Local Proxies to Early Universe Galaxies

• Large, gas-rich galaxies formed after the 912 Å 1216 Å first dwarf galaxies (hierarchical structure Lyman break technique 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 Pettini (2003): Courtesy of Kurt Adelberger velocity dispersion, metallicity, SFR � of SF Galaxies �

Brorby, Kaaret, Mirabel, & Prestwich (2016) �

g o l • Evidence for � − SFR − Metallicity Plane log SFR

BCD (Brorby+2014)

BCD Upper Limit Douna+2015 (Brorby+2014)

Spiral/Irregulars (Mineo+2012) LBA (Brorby+2016) � = 0.34 dex

12 + log(Ο/H) � of SF Galaxies Brorby, Kaaret, Mirabel, & Prestwich (2016)

• Evidence for � − SFR − Metallicity Plane

BCD (Brorby+2014)

BCD Upper Limit Douna+2015 (Brorby+2014)

Spiral/Irregulars (Mineo+2012)

LBA (Brorby+2016) ULX population and total X-ray luminosity are enhanced at lower metallicitiesin SF galaxies.

Mapelli+2010 Prestwich+2013 Walton+2011 Do spectral properties change with metallicity?

• 71% of flux from sources with � ≥ 10 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, � = 6.0 keV Γ = 0.8, � = 2.1 keV z = 6

Kaaret (2014) Spectral Shape of X-ray Binaries • Low, hard state vs high, soft state I Zw 18 X-ray Spectra (Chandra & XMM-Newton) ULX • � ≤ 10 erg s � = 1×10 erg/s

� = 3.3×10 erg/s High flux, soft thermal emission

Low flux, hard power law

Kaaret & Feng (2013) VII Zw 403 X-ray Spectrum (Suzaku) Observations

• Observed for 88.66 ks power-law fit • Spectrum is fit using a soft disc component and a hard Comptonizationcomponent. • Parameters: Disc temp: �� = 0.09 keV - e coronal temp: �� = 2.2 keV � = 11.4 Coronal optical depth: Comptonization (compTT) • � = 1.7×10 erg s • Fully consistent with hard ultraluminous state

Brorby et al. (2015) Suzaku Observations VII Zw 403 X-ray Spectrum (Suzaku) Brorby, Kaaret, & Feng (2015) • BCD: VII Zw 403 hosts ULX • Spectrum is fit using a soft disc component and a hard Comptonizationcomponent. • Parameters: Disc temp: �� = 0.09 keV - e coronal temp: �� = 2.2 keV Coronal optical depth: � = 11.4 • � = 1.7×10 erg s • Fully consistent with hard ultraluminous state Brorby et al. (2015) Suzaku Observations VII Zw 403 X-ray Spectrum (Suzaku) Brorby, Kaaret, & Feng (2015) • BCD: VII Zw 403 hosts ULX • Spectrum is fit using a soft disc component and a hard Comptonizationcomponent. • Parameters: Disc temp: �� = 0.09 keV - e coronal temp: �� = 2.2 keV Coronal optical depth: � = 11.4 • � = 1.7×10 erg s • Fully consistent with hard ultraluminous state Brorby et al. (2015)

Sutton et al. (2013) I Zw 18

• Observed with Chandra and XMM- Newton

• HST image in F675W band. • X marks dynamical center • + is location of X-ray source

Brorby et al. (2015) Two BCD Galaxies Containing ULX ULX-like vs BHB-like I Zw 18 X-ray Spectra (Chandra & XMM-Newton) VII Zw 403 X-ray Spectrum (Suzaku) � = 0.019 �⊙ � = 1×10 erg/s � = 0.062 �⊙ High, soft state

� = 1.7×10 erg/s � = 3.3×10 erg/s Hard, ultraluminous state Low, hard state

Brorby et al. (2015) Kaaret & Feng (2013) Holmberg II & IX Two more low-Z galaxies

Metalicity of ∼ 0.2 �⊙ (Egorovet al. 2013). � ∼ 0.4 �⊙ (Makarova et al. 2002) � = 0.1 �⊙ (Morales-Luis et al. 2011)

X-1 +

M81 X-1

DSS2 optical HEALPix survey, color (R=red[~0.6um]/G=average/B=blue[~0.4um]) GALEX:GII; NUV; PI:John Huchra 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) Cutoff power law Holmberg II X-1 � ∼ 0.2 � (Egorovet al. 2013). ⊙ Holmberg IX X-1 Suzaku � = 0.1 �⊙ (Morales-Luis et al. 2011) � ∼ 0.4 �⊙ (Makarova et al. 2002) Holmberg IX X-1 The ULX is located inside an association Part of a loose cluster of young stars. +

M81 Holmberg II X-1

GALEX:GII; NUV; PI:John Huchra

The ULX is located in a dense star-forming region of the galaxy which may indicate a dynamical center dynamically formed IMBH

Brorby et al. (2015) Ott et al. (2005) Walton, Middleton, Rana, et al. (2015) Walton, Miller, Harrison, et al. (2013) Holmberg II X-1 Holmberg IX X-1

Straight power law

XMM-Newton (pn, MOS) NuSTAR (FPMA, FPMB) Suzaku (FI-XIS, BI-XIS) Cutoff power law

VII Zw 403 X-ray Spectrum (Suzaku) I Zw 18 X-ray Spectra (Chandra & XMM-Newton)

IMBH candidate?

Kaaret & Feng (2013) Brorby et al. (2015) Summary of observational studies

• ULX population and total X-ray luminosity are enhanced at lower metallicitiesin 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. 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 M⊙ pc ) star clusters (e.g., Mapelli+2016) • Low metallicity -> weak winds -> massive stars + denser cluster core -> more interactions High Mass X-ray Binaries A Short History Lesson Roche lobe overflow

• N and � are related to the SFR of the galaxy (or starburst region) • First suggested from analysis of normal galaxies observed with Einstein Observatory (Giacconi+1979) • A strong correlation was found between X-ray and FIR emission of late-type star-forming galaxies Wind-fed accretion (long list of refs, p.343 Fabbiano 2006 ARA&A) • Has been confirmed by analyses of ROSAT observations (Read & Ponman 2001; Lou & Bian 2005, etc.) and Chandra/XMM-Newton (Ranalli+2003; Grimm+2003; Kaaret+2008, etc) • HMXBs dominate non-nuclear X-ray emission in galaxies where star formation is most violent. What determines the number of ULXs?

As an extension of HMXB population Initial Mass Function # of High (IMF) Mass Binaries Star Formation # of ULX (SFR) Common envelope survivability Binary and stellar Fraction wind strength Mineo et al. (2012) and Separation # of High IMF Mass Initial Mass Function (IMF) Binaries SFR # of ULX CE Phase • Binary and Makes the Main Sequence Fraction and Winds • Seems to be universal Separation Luminosity

Temperature Crosby et al. 2013) http://zebu.uoregon.edu/textbook/sc.html # of High IMF Mass Initial Binary Fraction Binaries SFR # of ULX CE Phase Binary and Fraction and Winds Separation • 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 �⊙. • Dependence on metallicity? Fraction of Star with Companions (%) Spectral type Figure from Raghavan et al. (2010). O-type: Mason et al. (1998a, 2009). B-A type: Shatsky & Tok ov inin (2002), Kobulnicky & Fryer (2007), Kouwenhoven et al. (2007) # of High IMF Mass More binaries survive common Binaries envelope phase at low metallicity SFR # of ULX CE Phase Binary and Fraction and Winds Separation

Dr. Andreas Irrgang: Dr. Karl Remeis-Sternwarte Bamberg Astronomical Institute of the University Erlangen-Nuremberg http://www.sternwarte.uni-erlangen.de/~irrgang Van den Heuvel & Heise (1972) # of High IMF Mass More binaries survive common Binaries envelope phase at low metallicity SFR # of ULX CE Phase Binary and Fraction Winds Linden+2010 and Separation

Belczynski+2010

© 2004 Thomson/Brooks Cole Low Metallicity -> Weaker winds Wind momentum – Luminosity relation (WLR) • 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 Decreasing metallicity mass loss and larger stars at end of life phase -> massive compact objects

Mokiem+2007 Mapelli, Zampieri, Ripamonti, & Bressan (2013) Compact object mass vs progenitor mass vs metallicity

Fryer, Belczynski, Wiktorowicz, et al. (2012)

Zampieri & Roberts (2009) 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) Linden+2010

Binary fraction distribution * Binary separation distribution *

� = �⊙ � = 0.1 �⊙ # of High IMF Mass Binaries

SFR # of ULX * CE Decreasing metallicity Phase Binary and Fraction and Winds Separation Mineo et al. (2012);Mineo et al. (2012)Brorby et al. (2014) 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)

∼ ��% solar

Linden+2010 Prestwich et al. (2013) Fragos+(2013) Brorby et al. (2016) Summary

• ULX populations are enhanced at low metallicities. • Simulations suggest more massive, close binaries (are ULX short orbital period binaries?) • Shape of X-ray luminosity function for ULX doesn’t significantly depend on metallicity (see Basu-Zych+2016 for further examination) • Normalization has metallicity dependence • ULX spectra have no known dependence on metallicity. • Simulations agree with observations of metallicity dependence. 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. 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 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 Outlook for the future (talks later this week will tell us more about this)

• Improved sampling of ULX properties across metallicity • Shorter period ULX (hours, days) -> close binary, RLO (increases at low-Z) • Age of star forming region is important • BH in primordial binary vs BH in binary due to 3-body interaction occurs over different timescales • M < 15 M⊙ + Age ∼ 10 Myr → stellar evolution (Mapelli+2013) • M > 15 M⊙ + Age ∼ 100 Myr → dynamical exchanges • More accurate metallicity measurements • Not averaged over galaxy and use ‘direct method’ from Ο III �4363 Å emission line • Lines from immediate region around ULX may also give hints about formation • Enhanced metallicity -> SN • Unchanged metallicity -> Direct collapse Conclusions/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 • Shape of X-ray luminosity function for ULX doesn’t depend on metallicity (see Basu- Zych+2016 for further examination) • Normalization has metallicity dependence • Outlook for the future (talks later this week will tell us this) • Improved sampling of ULX properties across metallicity • Shorter period ULX (hours, days) -> close binary, RLO (increases at low-Z) • Spectra showing strong outflows -> Accretion mode???QQQ -> Supercritical StMBH??? • Pinto, Middleton, & Fabian (2016): Resolved atomic lines reveal outflows in two ultraluminous X-ray sources • Age of star forming region is important • BH in primordial binary vs BH in binary due to 3-body interaction occurs over different timescales??? • 10 Myr vs 100 Myr? QQQ (Mapelli+2013) • For close binaries, stellar evolution of companion is faster than 3-body interaction rate (Next slide) • More accurate metallicity measurements: Not averaged over galaxy and use ‘direct method’ • [O iii]λ4,363Å THANK YOU