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Galaxy topics (1) 1. Gas in galaxies 2

Galaxy topics (1) 1. Gas in galaxies 2 2. Extended HI disks 31 3. Starburst, AGN winds, formation of disk galaxies 39 4. Galactic warps 48

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Galaxy topics (1) 1. Gas in galaxies 2

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  1. Galaxy topics (1) 1. Gas in galaxies 2 2. Extended HI disks 31 3. Starburst, AGN winds, formation of disk galaxies 39 4. Galactic warps 48 5. Galactic rings 53 Galaxy topics (2) 5. Clump cluster galaxies, disk formation 79 6. Chemical tagging 63 7. Supermassive black holes 67 8. Bulges 74 9. More on early-type galaxies 115 10. DM in galaxies 129

  2. 1. Gas in Galaxies Gas content, missing baryons, gaseous halos, baryon acquisition, gaseous halos as fuel source, metallicity of gaseous halos, cold halo gas and the missing baryons.

  3. HIPASS Sakai et al 2000 M33 MV = -12.5 MW Gas in galaxies now: star-forming galaxies Star-forming galaxies with MB < -18 typically have more mass in (cold) gas than in stars. Gurovich et al 2010

  4. At the low mass end, the baryonic TF law shows that gas-rich galaxies have baryons in relationship to the mass of their DM halos as measured by the circular velocity. McGaugh 2011

  5. At the very low mass end, the various dSph galaxies have a wide range of stellar masses going down to < 1000 M in some ultrafaint systems: M/L ratios > 1000, very low visible baryon content The dSph are now devoid of gas, although some have had recent star formation history. They show a stellar mass - metallicity relation similar to the gas-rich dwarf irregulars. The outcome of the SFH and chemical evolution in dIrr and dSph galaxies seems similar, although dIrr are still forming stars and the dSph are not. Did the faintest dSph lose most of their baryons via feedback or stripping, or did they never acquire their share ? Does the baryon acquisition become stochastic at some level in the DM hierarchy ?

  6. dIrr and dSph objects share the same relation, though their baryon contents are now very different. Mateo 2008

  7. The baryon content of the Milky Way The universal baryon / DM = 0.17 In the Milky Way, the ratio (stellar mass) / (dark matter mass) = 0.03 A small fraction of the Galactic baryons is in cold gas in the disk. With current star formation rate, believed to have been roughly constant for several Gyr, the disk will use up its cold gas in a few Gyr. Dark matter mass ~ 2.1012M, stellar mass ~ 6.1010 M. We are missing about 3.1011M of baryons: this represents about 80% of the Galaxy’s share of the baryons. Were they lost, or never acquired ? The rest of the baryons may be in the gaseous halo of the Galaxy: a potential reservoir for feeding ongoing star formation. Halo is believed to include gas over range of temperature, from the virial temp (~ 2.106 K, see as X-ray emission and OVI,OVII absorption lines) down to HI.

  8. Grcevich & Putman (2009): dwarf galaxies with D < 270 kpc are not detected in HI. Believed to be stripped by MW’s warm halo

  9. The presence of the Galactic warm/hot halo is consistent with non-detection in HI of the dwarf galaxies within R = 270 kpc (eg Grcevich & Putman 2009). Their gas is stripped by ram pressure + internal heating. The gas-rich dIrr galaxies lie at R > 270 kpc. Density of halo > 2-3.10-4 cm-3 out to R at least 70 kpc. (Gas contribution to hot halo from stripped dwarfs is small) HI high velocity clouds around the MW: morphologies show head-tail structure, suggesting interaction with halo medium which extends out to at least 50 kpc (Putman et al 2011)

  10. All of the missing baryons may not lie in the hot halo. eg Anderson & Bregman (2010): dispersion measure of LMC pulsars, lack of X-ray emission from large spirals and lack of OVII absorption by halos suggests that halos have only a fraction (~ 10%) of the missing baryons. The rest may have been expelled during galaxy formation or were never acquired by the DM halo. Supported by Anderson & Bregman (2011, 2016) detection of X-ray emission from the (morphologically) disturbed giant spiral NGC 1961 (Vc > 400 km s-1). Galaxy has cold gas content (HI + molecular) of about 8.1010M. Its total halo mass ~ 1-3.1011 M which is only a fraction of its share of the missing baryons. The cooling rate is ~ 0.4 M yr -1 which is much less than the gas consumption rate (~ 3 M yr-1). Combes et al 2009

  11. recombination reionization State of intergalactic medium with redshift The IGM as a function of redshift: neutral fraction McQuinn2016

  12. recombination reionization dwarf galaxies form here The IGM as a function of redshift: gas temperature massive galaxies form here McQuinn2016

  13. z = 6.42 The Gunn-Peterson effect: Ly photons in spectra of quasars are absorbed at high z because universe is not so ionized. z = 6.00 z = 5: Ly at 7300 A z = 6: Ly at 8500 A low Ly transmission at 8500A suggests that reionization is not yet complete by z ~ 6 z = 5.74 Fan 2006

  14. How do the baryons get into the galaxies ? Before about 2000, gas was believed to fall into the galaxies as the halo was being built up. The gas clouds virialize and the gas is shock-heated to a temperature corresponding to its virial velocity. T ~ V 2 : for V = 200 km/s, T ~ 2.6 x 10 6 K This gives a hot halo of gas. The MW has such a hot halo. Getting gas out of this hot halo into the disk to form stars is not so easy. Since about 2003, belief is that this is still true for the very massive DM halos (hot halos are seen in massive galaxies), but accretion in filaments of cold gas through the hot halos is more important for galaxies with M < 2-3. 1011 M (Dekel et al 2009)

  15. Paradigm for baryon acquisition Most of the baryonic mass in galaxies with halo masses < 2-3. 1011 M is acquired through filamentary cold-mode accretion of gas that was never shock-heated to its virial temperature (eg Birnboim & Dekel 2003, Keres et al 2005, 2009). Atmospheres of hot virialized gas develop in halos above 2-3.1011 M but cold accretion persists (especially at z > 2) and is the main driver of the cosmic SFH. Keres et al 2009

  16. How to get the hot gas from the halo into the disk to fuel star formation (and how to get it out of the disk back into the halo) High Velocity Clouds: (infalling HI clouds around the MW), long believed to be gas fuel source for the disk. Their formation is not completely understood yet. Their metallicities are ~ 0.2 Z (eg Sembach 2004)

  17. Condensation of HVCs from hot halo via thermal instability (Maller & Bullock 2004). Difficult to make this work in linear theory - would be mostly suppressed by buoyancy and thermal conduction (Binney et al 2009). Simulations of non-linear perturbations (overdensities 10-20) can generate cool clouds from hot halo if cooling time is shorter than the dynamical time. Otherwise clouds are disrupted by Kelvin-Helmholtz (shear) and & Rayleigh-Taylor (buoyancy) instabilities (Joung et al 2012) Only larger clouds (~ 105 M) can survive the trip from halo to disk. Smaller clouds lose their HI over ~ 10 kpc of travel and may become part of warm ionized Galactic disk.

  18. Keres & Hernquist (2009) simulations: at high z, gas is accreted from intergalactic medium in cold filamentary infall. At later times, densities are lower and filamentary flows are disrupted in inner regions of massive halos. Disrupted filaments are still able to supply cold gas to MW-sized galaxies. Cooling and Rayleigh-Taylor instabilities produce cold (< 104 K) clouds. Again, process needs seeding with moderate overdensities from the filamentary gas.

  19. Interaction of hot halo gas with infalling satellites : is this a significant source of fuel ? Cosmological hydro simulations provide a guide: simulations (Fernandez et al 2012) of a MW-sized galaxy shows that the amount of HI present in the halo since z = 0.3 is roughly constant, at about 108M.The HI accretion rate on to the disk is about 0.2 M yr -1. The satellites are losing gas (about 0.06 M yr -1) so other sources are needed to fuel the current star formation rate. Most of the cold gas in the halo comes from filamentary flows - much of it does not make it directly to disk but some is able to cool and form clouds. Gas stripped from satellites provides a fraction of the cold halo gas. Kauffmann et al 2012 agree: from study of isolated central galaxies (SDSS), accretion rate of gas from satellites is too small to feed the current star formation rate in the primary galaxies. SFR in primary galaxies correlates with the amount of gas in satellites - maybe the satellites are tracing a larger reservoir of ionized gas that is accreting on to the primaries. ,

  20. Entraining of hot halo material by galactic fountain: SN-driven accretion NGC 891 Fraternali et al (2001 ff) : very deep HI observations found halo HI in NGC 2403, 891, 4559, 6946 lagging rotation of the disk. In NGC 891, halo HI is detected to z = 22 kpc from the galactic plane. Lag in rotation relative to disk suggests that fountain gas loses angular momentum to the hot halo.

  21. Binney, Fraternali, Marinacci et al (2006 ff) propose that SN-driven fountain gas entrains hot halo material which returns to the disk. Star formation sustains itself from the hot halo, with accretion rate ~ 2 M yr-1 in the Milky Way. (Deposition rate is smaller than the overall rate of interchange of mass between disk and halo). Cool clouds are ejected from the disk into halo : Kelvin-Helmholtz instability strips gas from the clouds, and coronal gas condenses in their wake and returns to the disk. Fountain gas loses angular momentum to the halo and spins up the halo, which still lags the cold disk by ~ 100 km s-1.

  22. Red Blue Diversion The blue cloud / red sequence dichotomy is closely reflected in the chemical properties of the gaseous halo out to 150 kpc. The dichotomy is seen in the colors of galaxies: the red ones are mainly passive (little or no star formation) and the blue ones are star forming. Evolution is believed to be mainly from the blue cloud to the red sequence as blue galaxies run out of gas or are quenched. But some galaxies may go the other way: red galaxies that have acquired gas and restarted their star formation. See NGC 5102 above. Kauffmann et al 2003

  23. IGM median Metals in the halos If the halos are at least partly from gas ejected from star formation sites in the disk, then they would also be a reservoir of metals. eg Tumlinson et al (2011) found UV OVI absorption in 27/30 galaxies with sSFR > 10-11 yr -1 and only 4/12 passive galaxies with sSFR < 10-11 along sightlines with projected radii up to 150 kpc. log M* = 9.5 - 11.5

  24. The halo O-mass and total gas mass is comparable with that of the ISM. In Tumlinson’s passive galaxies, the gas may have been stripped, re-accreted or have cooled (or heated) so that the OVI is undetectable The gaseous halo may be a basic component of star forming galaxies that is removed or transformed when star formation is quenched (I.e. turned off). cf the Fraternali & Binney 2008 mechanism of halo gas entrainment: star formation drives the entrainment which then feeds the star formation. What is mode of quenching in this picture - what stops the star formation ? Mergers ?

  25. Where does the warm halo oxygen come from ? The O was likely produced by star formation in the disk and ejected into the CGM. Only 0.3 Gyr of SF at the present rate would be enough to produce it if it were all ejected. It could have accumulated over many Gyr, or be left over from early starbursts. An estimate of [O/Fe] (or other Fe-peak element) In the gaseous halo could give some constraint on when enrichment occurred. If the mass-metallicity relation of galaxies is associated with ejection and inflow of metals, (eg Davé et al 2011), then ejected material in lower-mass galaxies may be locked in the CGM and may return later to affect their chemical evolution. The apparent lack of chemical evolution of the Galactic disk over the last ~ 10 Gyr may also be due to enriched disk gas going into the CGM rather than directly into new stars (Martig) The ejected material may also feed the extended non-star-forming HI envelopes seen in many isolated disk galaxies and raise the abundances of these envelopes to their observed level (> 0.2 Z - eg Werk et al 2010, 2011). The Fraternali-Binney circulation could be a way to feed the outer HI envelopes with enriched material.

  26. Now know that there is a substantial amount of low density, cool (~104 K) HI in galactic halos (Prochaska et al 2017) : observed in Ly-limit absorption with COS/HST at z ~ 0.2 against QSOs  912 A (log NNI = 17.10 is too low to be detectable via the 21 cm line) Prochaska et al 2017

  27. 13 galaxies at z ~ 0.2 NHI vs projected radius Prochaska et al 2017

  28. 13 galaxies at z ~ 0.2 Metallicity histogram: wide spread from -2 to +1 Prochaska et al 2017

  29. cold accretion streams winds, outflows, tidally stripped gas Lyman Limit systems at z < 1 seen against background QSOs: metallicity of the cool (~ 104 K) CGM Lehner et al 2013

  30. 13 galaxies at z ~ 0.2 integrated mass of CGM vs projected radius integrated mass of cool CGM (~ 104 K) ~ 1011M Adding the mass of hot CGM would get close to the missing baryon mass. Prochaska et al 2017

  31. 2. The extended HI disks of disk galaxies Many disk galaxies are immersed in a vast extended disk of HI Examples NGC 2903 Irwin et al (2009) Vc = 190 km s-1 Outer contour 3.1017 cm-2

  32. NGC 2915 Meurer et al 1996 MB = -16 Vc = 80 km/s Abundance Z ~ 0.4 Z in outer disk HII regions (Werk et al 2010)

  33. NGC 5055 Battaglia et al (2006) weak warp, weakly lopsided: inner HI dominated by stellar disk, outer HI by DM. Some star formation in outer HI. Vc = 206 km/s.

  34. M83 outer HI (Bigiel et al 2010a) Some star formation, but depletion time ~ 100 Gyr in outer regions: outer HI is available as reservoir for star formation in inner regions. Is this reservoir utilized via radial flows ? HI UV, HI

  35. M83 outer HI Bigiel et al 2010a Short HI depletion time in inner disk Long HI depletion time in outer disk

  36. Diversion: Toomre Q (Toomre 1964) An axisymmetric disk is stable to axisymmetric perturbations if where  is the epicyclic frequency, cs is the sound speed and • is the surface density. A high sound speed (or velocity dispersion) stabilises the disk. Although Q < 1 is a criterion for largescale axisymmetric instability of the disk, it seems to be related to the smaller scale star formation threshold in disks of spiral galaxies (not a very secure result).

  37. Very low star formation efficiency in outer regions of HI disks Bigiel et al 2010b : 17 spirals 5 dwarfs SF efficiency drops for lower HI column density. Depletion time ~ 100 Gyr in outer regions. In outer regions, SF efficiency not strongly correlated with local Q Stabilized by DM ? (cf Schaye 2008)

  38. Radial Flows and chemical evolution Expect slow (~ 1 km/s) radial inflow in disk as consequence of infall of matter with angular momentum < that of local circular velocity (eg Lacey & Fall 1985). Could also be driven by bar, spirals, viscosity. Not possible to detect observationally (Wong et al 2004: NGC 5055; Elson et al 2011: NGC 2915): intrinsic asymmetries and warps in HI disks mask radial flows < 5-10 km/s. Spitoni & Matteucci (2011) looked at chemical evolution of disk with inflow. Goal is to reproduce an exponential stellar disk and this observed abundance gradient in the gas. Succeed with infall velocity increasing with radius and radially dependent infall rate decay time (~ 8 Gyr at sun). Not unique: other ways to get there without radial flow. Related study by Schoenrich & Binney (2009) invoked radial gas flow and radial stellar migration and stellar heating prescription. Reproduced abundance gradient, solar n’hood stellar MDF, bimodal alpha-Fe relation from migration rather than SFH, (Black points are mean of HII & PN)

  39. 3. Starburst- and AGN-driven winds, formation of disk galaxies Metal ejection from star-forming disk, enriches halo, returns gas to disk (maybe with extra entrained gas from halo). Believed to be essential part of understanding the mass-metallicity relation enrichment of IGM … Observations of winds driven by starbursts and AGNs at low-z (Sharp & Bland-Hawthorn 2010). See large-scale wind cone of enriched material with velocities of 100-200 km/s, accelerating to increasing heights above plane, originating from the region of active star formation. The material seen in the winds is not the winds themselves which are believed to be hot - we see the cooler material that is entrained in the wind. M82 wind: red is H From Veilleux et al 2005

  40. The difficulty of forming large disk galaxies with small bulges (recall Abadi et al 2003) led to current ideas on importance of suppressing early star formation, removing baryons from forming galaxy via massive winds and returning them slowly (Binney Gerhard Silk 2001, Governato, Gibson ….) UGC7321 Matthews et al (1999) The mass loss avoids loss of baryonic angular momentum to the assembling lumpy DM halo which leads to disks that are too small and violate the TF law. It also suppresses the steep DM cusps which are ubiquitous in CDM simulations but are not observed in galaxies.

  41. In the current simulations, galaxies start with more low-J material than they end up with. The surplus is ejected as wind. The halo absorbs some of the angular momentum and expands. Disk forms later from higher-J material which falls in: this suppresses the formation of large bulges which always occurred in earlier simulations (e.g. Abadi et al 2003). How much of this is true - what are the details ? Current simulations show these effects (eg Brook et al 2011 ff) in context of earlier discussion of winds, hot halo.

  42. The angular momentum content of disks (the M-J relation) is a critical constraint on formation mechanism (eg Fall 1983, Romanowsky & Fall 2012). Angular momentum per unit mass vs mass J ~ M 0.6 where J is the specific angular momentum i.e. the angular momentum per unit mass. Where does this scaling relation come from ? Where does angular momentum come from ?

  43. Brook et al (2011) on the formation of bulgeless galaxies. High resolution cosmological SPH simulations, enough resolution to resolve star forming regions. Adopt a high threshold density for SF: increases energy released into gas affected by SN feedback. In summary • low-J material accreted and rapidly expelled early. Later accreted material has higher-J and forms disk • reservoir of high-J material exists beyond star forming region • outflows occur perpendicular to disk. • Material that builds disk is accreted from outer regions near the galactic plane • mergers which cause gas to lose angular momentum trigger starbursts which expel much of the low-J gas. (May also expel gas which has lost angular momentum through secular processes) Loss of low-J material suppresses bulge formation

  44. gas blown out HI Angular momentum distributions of gas and stars within rvir at z = 0 Blown-out gas has low-J Brook et al 2011

  45. Simulation: B-band surface brightness and HI contours (1019 to 1022 cm-2) at z ~ 1.2. Extended HI relative to star forming region. mag arcsec-2 Brook et al 2011

  46. Outflowing gas Gas at z = 0.5 which will form stars by z = 0 All gas at z = 0.5 Disk is seen edge-on. Gas which feeds SF is near plane of the disk. Outflowing gas is perpendicular to plane. Brook et al 2011

  47. Maccio et al 2012 show how the heating of the DM cusp via the outflow can erase the central cusp in the DM distribution, as many have suggested. Low feedback High feedback

  48. 4. Galactic Warps Misalignments of inner and outer HI disks in disk galaxies are very common. Almost all galaxies with extended HI disks show kinematic or structural warps Early ideas about warps involved waves and modes in disks. After DM was discovered, external torques, misaligned angular momenta of gas components, gas and DM, and gas infall became more prominent. The very flat stellar disk and the warped outer HI disk may indicate different episodes of gas acquisition Rules about warp geometry (eg Briggs 1990): the inner HI disks are flat and aligned with the stellar disk out to the edge of the stellar disk. Then the warp begins - out to about R26.5 the line of nodes (LON) of the warp does not rotate with increasing radius. Beyond R26.5 the LON mostly advances in the leading sense. See v.d.Kruit & KCF ARAA 2011 for more on structure of warps

  49. Ideas about origin of warps • misalignment of stellar disk and the DM (Dekel & Shlosman 1983) • outer disk torqued by misaligned cosmic infall (eg Ostriker & Binney 1989 Shen & Sellwood 2006) • tidal interactions and minor mergers (eg Martinez-Delgado et al 2009) • misalignment of inner disk and outer hot halo: halo torques infalling cold clouds and aligns their angular momentum with that of the hot halo (Roskar et al 2010) . Are warps long-lived ? This would help to distinguish whether they are associated with misaligned dark matter or misaligned inflow or hot halo.

  50. About 65% of edge-on stellar disks also show weak warps which are sometimes asymmetric in their onset (eg Saha et al 2009, Guijarro et al 2010). The stellar warps may be tidal in origin, or come from the response of the stellar disk to the outer gas warp, or be part of the (infall-generated) warp. If the latter turns out to be correct, then it may be possible to use the stars to do chemical studies on the infallen material.

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