EXPLORING STAR-FORMATION & INHOMOGENEITY IN PRISTINE - PowerPoint PPT Presentation

EXPLORING STAR-FORMATION & INHOMOGENEITY IN PRISTINE ENVIRONMENTS: IFU STUDIES OF METAL-POOR DWARF GALAXIES Bethan James Nimisha Kumari, Sergey Koposov, Dan Stark, Kristy McQuinn, Vasily Belokurov, Max Pettini Alessandra Aloisi, Svea Hernandez Yiannis Tsamis, Mike Barlow, Mark Westmoquette Small Galaxies, Cosmic Questions: Durham July 2019

Outflows Accretion Are dwarf galaxies Are star-forming galaxies Galaxy Evolution chemically homogeneous? chemically homogeneous? Star-Formation Metal Distribution 109 spirals, 49 SF galaxies (Ho+2014) Metallicity Yuan+ 2011 Metallicity gradient Negative gradients → inside-out growth, flattening with time Positive gradients → tidal mixing, interacting systems (low-z) Dekel+ 2009 → infall of pristine gas into center (high-z) → SNe blowout + fallback, metal mixings?, self pollution? Small Galaxies, Cosmic Questions Bethan James

LESSONS FROM CHEMICAL How is star- VARIATIONS IN DWARFS…. formation triggered? Haro 11 (James+ 2013a) Nearby Dwarf XMP Dwarfs 5” ~ 1.8 kpc Sanchez-Almeida+, 2014 Knot B Knot C Knot A N Accretion of pristine gas → star-formation Small Galaxies, Cosmic Questions Bethan James

metal mixing timescales Star-formation ♻ James et al. 2010 Small Galaxies, Cosmic Questions Bethan James ⋍ stellar age gradient Metallicity gradient LESSONS FROM CHEMICAL VARIATIONS IN DWARFS…. n a 0.3 l a c i s y h P : l . a t e o 0 r 6 e b . I 0 - l − a e r n o M . A ) 5 2 8 O . 2 0 N − Monreal-Ibero et al. 2012 ( log (N/O) (N2S2) ) O / N ( g o l 0 1 young (WR) cluster . 1 − Self-pollution + 6 5 3 N/O . 1 − + ) c 4 0 6 . 1 (Westmoquette, James et al. 2012) e − s c r 6 a 2 − + ( 4 − y + e.g. NGC5253 2 0 Δ − 6 . 0 ) − c 0 0 e s c r a 2 ( x Δ ) 5 2 S 8 4 2 . 0 N − ( ) O / N ( g o l 0 1 . 1 − 6 5 3 . 1

LESSONS FROM SMALL SCALE Star-formation CHEMICAL VARIATIONS IN DWARFS…. efficiency James et al., 2016a, ApJ Mrk 71 Teyssier, Chapon & Bournaud 2010 Star-formation efficiency Hot stars Ionisation H α Surface Gas Density WFC3 Metallicity ‘image’ HeII emission from WFC3 narrow band imaging 1 pixel < 1pc Wolf Rayet stars 1 pixel < 1pc Chemical variations on <10pc scales Thermal instabilities → gas fragmentation Small Galaxies, Cosmic Questions Bethan James

BLUE DIFFUSE DWARF GALAXIES James, Koposov, Stark, Belokurov, McQuinn et al. 2015a, 2017 ‣ SDSS-search based on Leo-P morphology ‣ ~120 previously unknown low surface brightness star-forming dwarf galaxies ‣ 25% are extremely metal poor (i.e. <0.1 Zsol) ‣ Random regions of active SF in diffuse continuum → akin to high- z systems ‣ 50/120 observed with MMT ‣ 7/120 observed with McDonald ‣ 1/120 observed with VLT/MUSE… Small Galaxies, Cosmic Questions Bethan James

HOW IS STAR FORMATION TRIGGERED IN BLUE DIFFUSE DWARFS? Stream-fed? Gas density too low for gravitational instability (dIrrs, Hunter+ 1998). Lelli+ 2014 Triggered by external processes? Internal factors? dIrrs: Zhang+ 2012 e.g. turbulence, stellar feedback Star-formation rate density (Elmegreen & Hunter 2006) How stable is the gas? Is it turbulent? Are there signs of accretion? Is there an older stellar population? Stellar mass density Small Galaxies, Cosmic Questions Bethan James Hierarchical star-formation (e.g. Elmegreen+ 2010)

λ =4650-9300 Å JKB18: MUSE OBSERVATIONS 300x300 spaxels 900,000 spectra 0.2” spaxels James, Kumari + 2019a, in-prep ~0.9” seeing H α H α H α 30 30 30 30 − 16 . 50 200 V elocity Dispersion ( kms − 1 ) − 16 . 75 log Flux ( erg s − 1 cm − 2 ) 20 Radial V elocity ( kms − 1 ) 20 20 20 − 17 . 00 180 10 10 10 − 17 . 25 10 arcsecs arcsecs arcsecs 160 0 0 0 − 17 . 50 0 − 17 . 75 140 − 10 − 10 − 10 − 18 . 00 − 10 120 − 20 − 20 − 20 − 18 . 25 − 30 − 20 − 30 100 − 30 − 18 . 50 − 30 − 20 − 10 0 10 20 30 − 30 − 20 − 10 0 10 20 30 − 30 − 20 − 10 0 10 20 30 arcsecs arcsecs arcsecs 1 spaxel~20pc Regions of star-formation in arm-like structures Disturbed velocity field → past merger? Uniform velocity dispersion → no evidence of outflowing gas Small Galaxies, Cosmic Questions Bethan James

JKB18: IONIZATION MAPPING 1.0 1.5 [OIII]/Hb 20 20 1.0 0.5 0.5 [OIII]/Hb 0.0 15 -0.5 15 0.0 -1.0 -0.5 10 10 -1 0 1 [NII]/Ha 5 5 -1.00 -0.75 -0.50 -0.25 0.00 [SII]/Ha 0 0 -5 -5 -10 -10 20 15 10 5 0 -5 -10 20 15 10 5 0 -5 -10 •Mostly photoionization •Gradients of high ionization mis-aligned with star-formation •Evidence of shocks/gas-interactions •No diffuse ionized gas

JKB18: METALLICITY MAP Z [ O 3 N 2] 30 8 . 6 20 8 . 5 10 8 . 4 Z (O3N2) arcsecs 0 8 . 3 − 10 8 . 2 − 20 8 . 1 − 30 8 . 0 − 30 − 20 − 10 0 10 20 30 arcsecs 1 spaxel~20pc •Evidence of ~0.5 dex chemical variations •Variations depend on the metallicity diagnostic, but larger than diagnostic uncertainties Small Galaxies, Cosmic Questions Bethan James

JKB18: INHOMOGENEITY? 1 HII region ~100pc 30 20 10 arcsecs 1 0 Direct Method − 10 − 20 − 30 − 30 − 20 − 10 0 10 20 30 arcsecs •Variations do exist outside the mean •Only small scale variations, considering random distribution of SF regions, stellar ages, gas velocity O3N2 Small Galaxies, Cosmic Questions Bethan James

30 JKB18: CAUSE/EFFECTS OF 20 10 CHEMICAL INHOMOGENEITY arcsecs 1 0 − 10 − 20 − 30 − 30 − 20 − 10 0 10 20 30 arcsecs Light-Weighted Age (Gyr) Metallicity Metallicity Age (Gyr) SFR (Msol/yr) No sign of pristine gas Gas is well mixed accretion no self-pollution or outflows What do simulations of low-mass galaxies show us at these scales? Can simulations see such small-scale metal variations? Small Galaxies, Cosmic Questions Bethan James

CHEMICAL VARIATION BETWEEN GAS PHASES HST-COS Survey of Local Star-Forming Galaxies (mostly BCDs) (34 Orbits in Cycle17, 33 Orbits Cycle 25, PI: Aloisi) James et al., 2014b, ApJ N I 1134.1, Si II & SIII 1190 Fe II 1142, Si II & FeII 1260 1134.4,.9 1143,44 P II 1152 MW Ly α Si II 1193 1200.2,1200.7 ~130 pc CIII 1175 ~150 pc emission S II 1250 S II 1253 N I 1199, Si III 1206 Ly α C II* 1335.6,.7 Si II 1304 OI 1302 Ni II 1317 C II 1334 Ni II 1370 Si IV 1393 Si IV 1402 Accurate line-of-sight abundances → Gemini-GMOS data (PI: James, Kumari et al. 2017, 2018, 2019) → Keck/CWI data (PI: Hernandez, due 2020) Small Galaxies, Cosmic Questions Bethan James

CHEMICAL VARIATION BETWEEN GAS PHASES New COS data allows for tailor made ICF models for each galaxy (Hernandez et al. 2019 in-prep) All elements (saturated) Neutral Gas Abundance To be continued with +45 galaxies in CLASSY (PIs Berg, James & Stark +, Cycle 27) Ionized Gas Abundance: Small Galaxies, Cosmic Questions Bethan James

CHEMICAL VARIATION BETWEEN GAS PHASES James & Aloisi 2018 Just Oxygen Ionised - Neutral Ionised - Neutral O/H in neutral Gas is well phase increases mixed, despite in high mass metallicity galaxies Metallicity N(HI) Amount of HI is Decrease in N(P), N(O) N(HI) metals only seen strong function at very low of metallicity metallicities Metallicity Metallicity Galactic outflows and/or SF inefficiency in most metal poor systems Small Galaxies, Cosmic Questions Bethan James

SUMMARY Dwarf galaxies are not always chemically homogeneous Chemical variations in dwarfs tell us about: • chemical mixing timescales • past interactions • accretion of metal-poor gas • star-formation mechanisms • galactic outflows • Self pollution...or complete lack of. Incorporating these variations into models is essential for accurate representation of galaxy evolution ...especially for dwarf galaxies