Surveys of Nearby Galaxies What Next? HST-ERS Daniela Calzetti - - PowerPoint PPT Presentation

Surveys of Nearby Galaxies – What Next?

Daniela Calzetti (UMass) and the LEGUS Team (Angela Adamo, Göran Östlin, Matteo Messa)

Surveys for All, Lund Observatory (Sweden), 1-2 February 2016

HST-ERS

The LEGUS Team

56 investigators (so far) at 30+ Institutions (US+EU):

• D. Calzetti (PI, UMass), J. Lee (Deputy PI, STScI), J. Andrews (U Arizona), A.

Aloisi, S.N. Bright, T. Brown, C. Christian, M. Cignoni, K. Levay, M. Regan, E. Sabbi, L. Ubeda, B. Whitmore (STScI), A. Adamo, M. Messa, G. Östlin (Stockholm U), R. Chandar (Utoledo), G. Clayton (LSU), D. Cook, D. Dale (U Wyoming), R. da Silva, M. Krumholz (UCSC), S. de Mink (Amsterdam U), C. Dobbs (UExeter), B. Elmegreen (IBM), D. Elmegreen (Vassar), A. Evans, K. Johnson (UVa), M. Fumagalli (U Durham), J. Gallagher, J. Ryon (UWisc), D. Gouliermis (MPIA), K. Grasha (UMass), E. Grebel, F. Shabani (Heidelberg U), A. Herrero, S. Taibi (IAC, Canarias), D. Hunter (Lowell Obs), L. Kahre, R. Walterbos (NMSU), R. Kennicutt (IoA, Cambridge), H. Kim (UT-Austin), D. Lennon (ESA),

• C. Martin, S. van Dyk (Caltech), P. Nair (U Alabama), A. Nota, L. Smith (STScI/

ESA), A. Pellerin (SUNY-Geneseo), J. Prieto (UC de Chile), D. Schaerer (Geneva Obs), D. Schiminovich (Columbia U), D. Thilker (JHU), M. Tosi, E. Sacchi (INAF-Ubologna), A. Wofford (IAP)

Red for Senior Advisory Group Blue for Science, Data Processing, EPO Leads

Across Time…

Cosmic SFR Mass Assembly

Madau & Dickinson 2014, ARAA Madau+1996

We are currently in a position to describe to some accuracy the evolution of SFR and mass assembly across cosmic times…

Across `Space’?

We can’t yet connect the two scales of galaxy-wide SF and individual stars/star clusters: § How do stars form? Always clustered? In a scale—free hierarchy? (Elmegreen et

• al. 2006)

§ Do we have one or two modes of star formation (clustered and diffuse)?

(Meurer et al. 1995, Crocker et al. 2014)

§ How has the mode of SF evolved with time? (109 Mo clumps at z~1) § How does SF power the ISM? § On what timescale do stars disperse? § What are the bound structures (star clusters) tracing? How do they evolve? § Do we have a universal stellar IMF? § How are `local’ SFRs affected?

NGC 628, ~10 Mpc, GALEX FUV+NUV

The über-questions:

1. How does the Hubble sequence form? 2. How is SF linked to the gas supply (Kennicutt-Schmidt Law)? 3. What is the role of feedback in shaping galaxies and regulating SF?

Image kindly provided by D. Thilker

The QuesCons

• The Physics of GalacCc-Scale Star FormaCon

– Mode(s) of star formaCon – Cluster-SF links – FormaCon and Erasure of structures – Links to dynamical structures, gas structures

• The Physical Underpinning of the IMF

– Is the IMF Universal? – What are the driving parameters/mechanisms?

The Schmidt-KennicuS Law

ΣSFR ~ (Σgas)

γ , γ=1, ..., 2

Σgas ΣSFR The value of γ is connected to the underlying physics of the scaling between star formaCon and gas (a.k.a. the SK Law).

KennicuS & Evans, 2012, Whole Galaxies Heiderman et al. 2010, Milky Way Molecular Clouds

However, the SK Law does not appear to be `scalable’ from whole galaxies to galaxies’ consCtuents (star forming regions, molecular clouds, etc.). Problems with SFR & gas measurements? (C+2012)

Changing of the dominant physics? (Hopkins+2013)

SFR Measures and Stellar Pops Diffusion

M101, ~7.5 Mpc GALEX FUV+NUV A common characteristic of local spirals: GALEX FUV-NUV color maps show that interarm regions have redder UV colors than arm regions This cannot be an effect of differential attenuation. Interarm regions in M101 do not contain stars younger than ~40 Myr (or more massive than ~10-15 Mo) (Crocker et al. 2015, HST UV)

Clusters Intercluster Light

In starburst galaxies, the intercluster light only shows evidence for B stars (no O stars, like clusters). IC light = 80% of all UV light. Dispersion of clusters (Tremonti et al. 2001,

Chandar et al. 2005) or two modes of SF (Meurer et

• al. 1995)?

The RepresentaCve Local Volume

Ø The Local Universe is over-dense relaCve to the cosmic average, by a factor of a few, up to at least ~10 Mpc. Ø Galaxies within the local 4 Mpc depart from the cosmic SFR for the most recent ~4 Gyr (Williams+2011) Ø The RepresentaCve Local Volume does not occur before 10 Mpc; need to be up to 100 Mpc, if U/LIRGs are included

Drozdovsky+2008 12

The LEGUS Project

Ø To make progress: investigate the spatially resolved SFHs and cluster formation histories of nearby galaxies with HST. Ø Cycle 21 HST Treasury Program: - UV-to-I imaging of 50 nearby (<18 Mpc) galaxies, targeting star clusters and resolved stars.

legus.stsci.edu

LEGUS footprint=magenta LEGUS parallels=blue Archival data=red First public release of Data Products: October 12, 2015:

hSps://archive.stsci.edu/prepds/legus/

C.+2015a

Star Clusters: Age+Masses via BB Photometry

5th band breaks degeneracy in SED fitting. UV more stable (~4X) than Hα for separating young, Qo-deficient from aging clusters, esp. at low cluster masses – add stochastic models

(Krumholz+2015) 3.15 Mpc

Clusters LFs, Γ, env. variations… Estimated numbers: ~ 30,000

UV, Masses, and Ages of Natal Clusters

NGC5253 – central nebula

Cluster 5, extremely young, and behind dust. AV ~ 1.9 mag.

Cluster 11: extremely young; ~3X less massive than earlier results. Still MV=-12.8, at the high-end envelope

• f the MV-SFR relation for star clusters.

Mixed with AV~50 mag dust. NO NEED for truncated IMF! The two clusters account for ~50% of the ionization in NGC5253. (and ~10 VMSs would account for it all, Smith+subm) C+2015, ApJ

Survival and DissoluCon of Clusters

– Cluster randomizaCon Cmescale at ~ 40 Myr in NGC628 – Mostly due to dissoluCon

• f star clusters
• 0.8
• K. Grasha+2015, ApJ, in press

NGC628, ~10 Mpc 50 pc non-clustered

>1200 star clusters idenCfied, divided into: 1. Symmetrical (red), older 2. Elongated (green) 3. MulCple Peaks (blue), youngest Analyze with 2p correlaCon funcCon

Bringing it all together

(caveat emptor: this is only 3 galaxies)

• M101: interarm populaCon consistent with stars

being older than 40 Myr (mass <10-15 Mo, Crocker+2015)

• ★ NGC6503: randomizaCon of stars occurs around

60 Myr (Gouliermis+ 2015)

• ★ NGC628: star clusters become randomly

distributed around 40 Myr (Grasha+2015)

Taken all together this would appear to suggest that at least a fracCon of the stars in the field originate from dissolving star clusters over ~40-60 Myr

(we already knew of `infant mortality’ at < 10 Myr!)

The Realm of JWST

• Address the physical founda/on of the

Schmidt-KennicuS Law (scaling between SFR and gas) via YSOs within 1 Mpc and dust- enshrouded HII regions within ~10 Mpc.

• InvesCgate the low-end of the IMF via

resolved counts out to ~0.5 Mpc (NGC6822). Current evidence gives 2x mass varia/ons for galaxies.

• SF Histories of galaxies between 200 Myr and

10 Gyr, out to ~6-8 Mpc for `fossil record’ studies (~a dozen giant spirals, and at most 1 giant ellipCcal).

• Physics of the Bulge mass – BH mass relaCon
• Physics of dust processing (e.g., PAHs) out to

~10 Mpc and of dust formaCon (e.g., CCSNe)

• ut to larger distances

KennicuS & Evans 2012 Geha+2013

8

The Realm of WFIRST (but also GAIA, EUCLID,…)

Milky Way SimulaCon (Rensselaer/ Benjamin A. WilleS/Heidi Newberg)

Fossil Galaxy Assembly: § Mergers of small satellites into larger galaxies is one of the main mechanisms of the hierarchical galaxy assembly in ΛCDM models. § The signs of these 10:1 mergers survive for mulCple Gyrs, in the form of streams, tails, bridges, etc. § The stellar populaCons that trace these features can be detected in external galaxies out to ~10-12 Mpc with WFIRST, similarly to what is done today from the ground for the MW/MCs/stream systems

10

The Far-Future: Outer Disk Physics

• Galaxies are far more extended

than their bright disks, in stellar populaCons and gas content.

• Regions with extreme condiCons of

density, pressure, metal enrichment, dust content, response to feedback.

• Outskirts are dynamically

`quiet’: imprints of structures persist for many Gyrs – testbeds for:

• Modes of star formaCon
• Upper IMF universality
• Star cluster evoluCon and internal

processes

• Key requirements: UV (SFH<200

Myr) +efficiency (FoV+sensiCv.)

Thilker et al. 2007 M83; 4.5 Mpc; GALEX+HI WFC3 FoV LUVOIR FoV (~5x WFC3) 23

Conclusions

1. A multi-pronged approach is required to understand the spatial (and not

• nly temporal) evolution of stellar populations in galaxies. LEGUS is

designed to address all of these, and will attempt to address:

• 1. Presence of multiple modes of SF
• 2. Cluster formation and evolution
• 3. Variations of the high-end of the IMF
• 4. Calibration of local SFR(UV); (e.g., resolved KS Law)
• 5. Dynamical evolution of galaxies – links of scales of SF
• 6. Models of formation of massive stars

2. Preliminary results include:

• 1. Clusters dissolve and contribute to the field population on timescales

beyond the `infant mortality’ one (40-60 Myr vs <10 Myr)

• 2. `Natal’ clusters can be detected at short (optical and possibly UV)

wavelengths.

BUT… We need a future UVOIR space facility that will address all of those quesCons across the many environments that may have been present at the Dawn of the Universe