– or: debunking the Neufeld scenario On the enhancement of the Lya equivalent width by a multiphase interstellar medium – or: debunking the Neufeld scenario Peter Laursen With Florent Duval & Göran Östlin (OKC) www.dark-cosmology.dk/~pela Dark Cosmology Centre | Niels Bohr Institutet | Københavns Universitet

Motivation Lyman α emitting galaxies (LAEs) are important probes of the high-redshift Universe: • Epoch of Reionization • Baryonic Acoustic Oscillations • Luminosity function (faint end) These are statistical properties. Individual observations are hampered by insufficient knowledge about radiative transfer effects. One way, however, to probe individual galaxies is by looking at the equivalent width of Lyα. They are a good tool because the Lyman-alpha bias, the propensity for galaxies to form in the highest overdensity of the underlying dark matter distribution, can be modeled and accounted for. Lyman-alpha emitters are over dense in clusters

Motivation Equivalent width: Boost: “Max 240 Å!”, say Charlot & Fall (1993), and Schaerer (2003). “But… but…”, say Kudritzki et al. (2000), Malhotra & Rhoads (2002), Rhoads et al. (2003), Dawson et al. (2004), Hu et al. (2004), Shimasaku et al. (2006), Ouchi et al. (2008), Nilsson et al. (2009), Kashikawa et al. (2011), etc. Boost: “Clumpiness!”, say Chapman et al. (2005), Finkelstein et al. (2007, 2008, 2009a,b,c, 2011a,b), Dayal et al. (2008, 2009, 2010, 2011), Niino et al. (2009), Yuma et al. (2010), Kobayashi et al. (2010), Blanc et al. (2011), Nakajima et al. (2012), etc.

Multiphase medium Neufeld (1991); Hansen & Oh (2006)

Neufeld 1991 Enter Hansen & Oh (2006)

Systematic approach MoCaLaTA (Laursen et al. 2009)

Varying the input parameters 3 1 cm-3 Z 0 km s-1 0 cm-3 Central 104 K; 106 K 100 pc “Fiducial” model: • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters (on at a time) • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

Varying the input parameters • Covering factor, fc • Cloud HI density, nHI,cl • Cloud dust density ( metallicity, Zcl) • Cloud velocity dispersion, σV,cl • Galactic outflow velocity, Vout • Intercloud HI density, nHI,ICM • Intercloud dust density ( ZICM) • Emission scale length, H • Emission/cloud correlation factor, Pcl • Intrinsic line width, σline • Gas temperature, Tcl; TICM • Cloud size distribution, rcl,min; rcl,max; β

From ideal to semi-realistic (varying in unison)

From ideal to semi-realistic (each dot is the result of a model)

From ideal to semi-realistic

From ideal to semi-realistic

From ideal to semi-realistic

Line profiles Average spectrum of boost-yielding (extreme) models — not realistic (too narrow)

Alternative scenarios • Top-heavy IMF (Malhotra & Rhoads 02) • Population III stars (Schaerer 03, Tumlinson 03) • Delayed escape of Lyα (Roy+ 10, Xu+ 11) • AGN activity (<5%, Wang+ 04, Gawiser+ 06) • Viewing angle (Laursen 07/09, Verhamme 12) • Cooling radiation (Dijkstra+ 09, Laursen+ 09, Dayal+ 10) • Measuring errors (Henry+ 10) • Star formation stochasticity (Forero-Romero & Dijkstra 12) • Inhomogeneous escape (Hayes+ 07)

Alternative scenarios • Top-heavy IMF (Malhotra & Rhoads 02) • Population III stars (Schaerer 03, Tumlinson 03) • Delayed escape of Lyα (Roy+ 10, Xu+ 11) • AGN activity (<5%, Wang+ 04, Gawiser+ 06) • Viewing angle (Laursen 07/09, Verhamme 12) • Cooling radiation (Dijkstra+ 09, Laursen+ 09, Dayal+ 10) • Measuring errors (Henry+ 10) • Star formation stochasticity (Forero-Romero & Dijkstra 12) • Inhomogeneous escape (Hayes+ 07)

Viewing angle (even in a homogeneous medium, without dust, a “boost” can be measured)

Alternative scenarios • Top-heavy IMF (Malhotra & Rhoads 02) • Population III stars (Schaerer 03, Tumlinson 03) • Delayed escape of Lyα (Roy+ 10, Xu+ 11) • AGN activity (<5%, Wang+ 04, Gawiser+ 06) • Viewing angle (Laursen 07/09, Verhamme 12) • Cooling radiation (Dijkstra+ 09, Laursen+ 09, Dayal+ 10) • Measuring errors (Henry+ 10) • Star formation stochasticity (Forero-Romero & Dijkstra 12) • Inhomogeneous escape (Hayes+ 07)

Conclusion: No astrophysically realistic scenario can boost the Lyα equivalent width by clumpiness alone. Rather, a combination of clumpiness, orientation, top-heavy IMF, cooling radiation, etc. adds to create a boost. • o r i e n t a c o l i n g r a d t Whereas in the scenario originally proposed by Neufeld the boost increases with cloud covering factor, even a small cloud velocity dispersion inverts this relation. •