Gas content and gas kinema/cs in low-mass galaxies Leslie Hunt - PowerPoint PPT Presentation

Gas content and gas kinema/cs in low-mass galaxies Leslie Hunt INAF-Osservatorio Astrofisico di Arcetri, Firenze

why low-mass (metal-poor) galaxies? UV luminosity func/onsz~4, z~8 � low mass galaxies are the most Bouwens+ 2011 numerous at all redshiGs, very low-luminosity galaxies provide the dominant contribu/on to the luminosity density at z> 6 (e.g., Bouwens+ 2011, 2012; Atek+ 2015; Sun & FurlaneUo 2016) Galaxy Stellar Mass func/ons to z~4 from Ilbert+ 2013, data from z~0 Moustakas+ 2013, Baldry+ 2012) � although dark-maUer haloes are built boUom-up, massive galaxies form their stars early Specific star forma/on rate as on (downsizing), unlike low- func/on of look- back /me for mass galaxies that form a large galaxies of frac/on of their stars later varying masses (Thomas+ 2010)

outline of talk � INEFFICIENCY of star forma/on/galaxy mass assembly and the role of FEEDBACK � feedback and gas/SFR scaling rela/ons (KennicuU-Schmidt) � scaling rela/ons for low-mass galaxies: gas frac/ons, mass, SFR, metallicity (take note of metal-poor starbursts) � feedback and the baryonic Tully-Fisher rela/on: contribu/on of molecular gas in low-mass (metal-poor) starbursts � pressure support and turbulence, comparison of different tracers in low-mass galaxies Low-mass galaxies important probe of galaxy forma/on scenarios because of their vulnerability to feedback

feedback and the inefficiency of galaxy mass assembly and star forma/on

stellar and baryon frac/on in dark-maUer halos star-forma/on efficiency (SFE) peaks at 5x10 11 M ¤ , characteris/c mass “sweet spot” for galaxy forma/on z=0 stellar mass depends on dark-maUer halo mass, but rela/vely independent of redshiG (lookback /me) Behroozi+ 2013a, 2013b (see also Moster+ 2013, Genel+ 2014)

feedback renders galaxy forma/on inefficient Stellar mass (M ¤ ) Stellar /baryonic “sweet spot” Stellar /baryonic at 5x10 11 M ¤ Stellar /baryonic Halo mass (M ¤ ) Hopkins+ 2014, FIRE simula/ons Halo mass (M ¤ )

feedback renders galaxy forma/on inefficient Stellar mass (M ¤ ) Stellar /baryonic models without feedback are in severe conflict with observa/ons, especially at low masses “sweet spot” Stellar /baryonic at 5x10 11 M ¤ Stellar /Baryonic Halo mass (M ¤ ) Hopkins+ 2014, FIRE simula/ons Halo mass (M ¤ )

feedback and gas scaling rela/ons

star forma/on is inefficient because of feedback stellar feedback injects sufficient momentum to offset dissipa/on; otherwise too- efficient cooling would cause all gas to collapse and form stars KennicuU-Schmidt (KS) law rela/ng SFR and gas surface densi/es; observa/ons (KennicuU 1998; Bigiel+ 2008; Genzel+ 2010; Daddi + 2010) indicated by yellow shaded region. Simula/ons including various recipes for feedback (see previous slide) shown by points. Instantaneous SFE (here SF per dynamical /me) in dense gas is 100%, but global SFE is ~2%. Hopkins+ 2014

inefficient star forma/on in metal-poor galaxies? lower intercepts for SMGs Genzel+ (2010) lines (with unit slope) SFGs Tacconi+ (2010, 2013) 10 3 BzKs Daddi+ (2010) in this plane mean Spirals Kennicutt (1998) 10 2 longer gas deple/on Starbursts Kennicutt (1998) 1Gyr Σ SFR [M sun yr − 1 kpc − 2 ] /mes 10 1 10Gyr starbursts and high-z 10 0 galaxies tend to have 10 − 1 shorter gas deple/on /mescales 100Myr 10 − 2 All resolved measurements (except Kennicutt) + (here α CO converted to 10 − 3 z l o common scale, e.g., h ) m 9 10 − 4 0 Genzel, Tacconi+ 2010) u False colors: Bigiel+ (2008) 0 r K 2 ( 10 0 10 1 10 2 10 3 10 4 Σ gas [M sun pc − 2 ]

inefficient star forma/on in metal-poor galaxies? high Σ SFR and high Σ HI SMGs Genzel+ (2010) common in blue compact SFGs Tacconi+ (2010, 2013) 10 3 dwarf galaxies (BCDs), and BzKs Daddi+ (2010) ● Spirals Kennicutt (1998) some LiUle THINGS dwarfs, 10 2 Starbursts Kennicutt (1998) despite their low metallicity 1Gyr Σ SFR [M sun yr − 1 kpc − 2 ] 10 1 10Gyr ● ● ● 10 0 ● ● ● ● 10 − 1 ● ● ● ● ● 100Myr 10 − 2 All resolved measurements ● (except Kennicutt) ● ● ● ● ● ● ● ● ● ● 10 − 3 ● ● ● ● ● ● Blue compact dwarfs (HI only) ● dwarfs may not all be ● ● ● ● ● ● ● ● ● ● LITTLE THINGS (HI only) ● ● ● ● ● ● ● inefficient at forming stars ● ●● ● ● SHIELD dwarfs (HI only) 10 − 4 ● FIGGS dwarfs (HI only) compare with high-redshiG VLA − ANGST dwarfs (HI only) popula/ons to consider the best local analogs 10 0 10 1 10 2 10 3 10 4 Σ gas [M sun pc − 2 ] Hunt+ in prep

inefficient star forma/on in metal-poor galaxies? high Σ SFR and high Σ HI Ruby (Canameras+ 2017) SMGs Genzel+ (2010) common in blue compact SFGs Tacconi+ (2010, 2013) 10 3 dwarf galaxies (BCDs), and BzKs Daddi+ (2010) ● ● Spirals Kennicutt (1998) some LiUle THINGS dwarfs, IIZw40 10 2 Starbursts Kennicutt (1998) despite their low metallicity 1Gyr Σ SFR [M sun yr − 1 kpc − 2 ] SBS0035 − 052 10 1 NGC1140 NGC5253 10Gyr IIZw40 from Kepley+ (2014, ● ● ● ● NGC1569 2016): rightmost es/mate 10 0 includes H 2 from ALMA; ● DDO87 IC10 ● ● ● 10 − 1 NGC5253, NGC1569, IC10 ● ● ● also include H 2 in rightmost ● ● 100Myr 10 − 2 point All resolved measurements ● (except Kennicutt) ● ● ● ● ● ● ● ● ● ● 10 − 3 ● ● ● ● ● ● Blue compact dwarfs (HI only) ● dwarfs may not all be ● ● ● ● ● ● ● ● ● ● LITTLE THINGS (HI only) ● ● ● ● ● ● ● inefficient at forming stars ● ●● ● ● SHIELD dwarfs (HI only) 10 − 4 ● FIGGS dwarfs (HI only) compare with high-redshiG VLA − ANGST dwarfs (HI only) popula/ons, some approach maximal starbursts 10 0 10 1 10 2 10 3 10 4 Σ gas [M sun pc − 2 ] Hunt+ in prep

low-mass galaxy resolved HI samples FIGGS (Faint Irregular Galaxies GMRT Survey): 65 faint dwarf irregulars (dIrrs) within D≤10 Mpc (Begum+ 2008; Rowychowdhury+ 2014; Patra+ 2016) LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey): 37 dIrrs, 4 Blue Compact Dwarfs (BCDs) within D≤10.3 Mpc (Hunter+ 2007; Hunter+ 2012; Zhang+ 2012; Oh+ 2015; Maier+ 2017; Iorio, Fraternali + 2017) VLA-ANGST (Very Large Array survey of Advanced Camera for Surveys Nearby Galaxy Survey Treasury): 35 nearby galaxies from the ANGST survey (OU+ 2012; Warren+ 2012; S/lp+ 2013a, 2013b, 2013c) SHIELD (Survey of H I in Extremely Low-mass Dwarfs): 12 galaxies selected from the ALFALFA survey having HI masses < 10 7 M ¤ (Cannon+ 2011; McNichols+ 2016; Teich+ 2016)

low-mass galaxy resolved HI samples Low-metallicity starbursts : 18 BCDs with measured star-forma/on histories (Lelli, Fraternali+ 2012a, 2012b, 2014a, 2014b); 18 BCDs with single-dish CO(1-0) IRAM detec/ons (Hunt+ 2015, in prep)

low-mass starbursts: scaling rela/ons of metallicity (O/H), star- forma/on rate (SFR), stellar mass (M star ), and gas frac/ons

local scaling rela/ons of stellar mass and SFR Local Volume Legacy (LVL, KennicuU+ 2008, Lee+ 2009, Dale+ 2009, Cook+ 2014) within 11 Mpc COLDGASS (CO, followup of HI sample, Saintonge+ 2011, Huang+ 2014) ● COLDGASS 0.9 LVL 10 − 7 0.8 0.7 10 − 8 SFR/M star 0.6 10 − 9 0.5 ● 0.4 ● ● ● 10 − 10 ● ● ● ● ● ● ● ● ● ● ● ● ● 0.3 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 0.2 ● ● ● ● ● ● ● ● ● ● 10 − 11 ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 0.1 ● ● ● ● ● ● ● ● ● ● ● 0.0 10 6 10 7 10 8 10 9 10 10 10 11 7.5 8.0 8.5 9.0 Gas 12+Log(O/H) M star fraction volume-limited samples also follow clear “main sequence” (Noeske+ 2007, Salim + 2007) of star forma/on (slope best fit to LVL sample, specific SFR SFR/M star : sSFR ~ M star -0.13 )