How do galaxies evolve into the forms they have today? Spheroid - PowerPoint PPT Presentation

How do galaxies evolve into the forms they have today? Spheroid Galaxies Disk Galaxies Hubble 1936 Susan Kassin (Space Telescope Science Institute) Raymond Simons (Johns Hopkins), Camilla Pacifici (STScI), DEEP2 & SIGMA Survey teams, VELA simulation team

Galaxies at a redshift of 1 (8 billion years ago) credit: AEGIS Survey

What are galaxies? NGC 4414, credit: HubbleSite.org NGC 1132; credit: Hubble Heritage

How and when are disks assembled? How & when do disks obtain their current well-ordered state? M63, credit: HubbleSite.org

Disk galaxies rotate under the influence of gravity -200 km/s NGC 7171 30” Weiner incl. Kassin et al. 2006 Sandage & Bedke 1988 +200 km/s Velocity map of a local disk galaxy

How and when do quiescent spheroids form? NGC 1132; credit: Hubble Heritage

Outline • Disk Formation “Mass of Disk Formation” o Assembly of disks over cosmic time o • Spheroid Formation Formation timescales vary with galaxy mass and redshift o • JWST observations of nascent galaxies

Background Models of Disk Formation and Evolution

Analytic Model of Disk Collapse 1. Angular momentum acquisition 2. Baryons collapse to a disk • Disks start off well-ordered • They grow in radius in an “onion skin” manner 3. Collapse from the inside out (onion skin) e.g., White & Rees 1978; Fall & Efstathiou 1980; Blumenthal et al. 1984; Mo, Mao & White 1998; Dalcanton, Spergel, & Summers 1997

Analytic & numerical theory: Tully-Fisher is tight Luminosity ~ Velocity 3 magnitude rotation velocity (km/s) e.g., Mo, Mao, & White 1998; Sales et al. 2017

Dynamical theory of isolated disk evolution Stars start off in a well-ordered and thin disk. Their velocity dispersion increases with time via: • Molecular clouds (e.g., Aumer, Binney, & Schönrich 2016) • Merging satellites (e.g., Velazquez & White 1999) • Buckling of bars (e.g., Debattista et al. 2006) Stellar velocity dispersion • Spiral structure (km/s) • Minor mergers (e.g., Moster et al. 2011) Time (Gyrs) Aumer, Binney, & Schönrich 2016

Analytic Theory of an isolated disk • Disks start off well-ordered and thin • They thicken with time • Disks lie on a tight Tully-Fisher Relation • Disks grow in radius in an “onion skin” manner We examine this picture with observations of galaxy kinematics at a range of redshifts.

Outline • Disk Formation “Mass of Disk Formation” o Assembly of disks over cosmic time o • Spheroid Formation Formation timescales vary with galaxy mass and redshift o • JWST observations of nascent galaxies

Galaxy kinematics from z=3 to now To study the evolution of galaxy kinematics, we need spectra and Hubble images for a hundreds of representative galaxies over a significant range in redshift and stellar mass. • Star- forming galaxies on the “main sequence” • No cuts on morphology • Spectra from DEEP2 & SIGMA Surveys (Newman et al. 2012, Simons, Kassin et al. 2017) • Hubble images from AEGIS & CANDELS (Davis et al. 2007, Grogin et al. 2011) • Total stellar mass is measured from multi-band photometry

Galaxy kinematics are measured from emission lines Simons, Kassin et al. 2016 z=2 Hα velocity dispersion 175 km/s velocity radius 70 km/s radius radius wavelength • We measure σ , which had not been done before, and V rot • We corrected V rot and σ for the effects of seeing, which had not been done before. • Slits are aligned to within 45° of galaxy major axes to measure V rot • We correct V rot for inclination using Hubble image Weiner inc. Kassin et al. 2006, Kassin et al. 2007, Covington, Kassin et al. 2010, Kassin et al. 2014

“Local” Tully -Fisher Relation at z=0.2 Tully- Fisher “Ridge - line” from Reyes et al. 2011 log rotation velocity V rot (km/s) log stellar mass (M ⦿ ) Simons, Kassin et al. 2015; also Bekeraite et al. 2016 (CALIFA), Bloom et al. 2017 (SAMI)

Ordered disks lie on ridge-line, Disturbed galaxies lie off of it

“Local” Tully -Fisher Relation (z~0.2) Simons, Kassin et al. 2015; also Bekeraite et al. 2016 (CALIFA), Bloom et al. 2017 (SAMI)

“Local” Tully -Fisher Relation (z~0.2) “Mass of Disk Formation” disks may not form disks will form Simons, Kassin et al. 2015; also Bekeraite et al. 2016 (CALIFA), Bloom et al. 2017 (SAMI)

Analytic Theory of an isolated disk • Disks start off well-ordered and thin • They thicken with time • Disks lie on a tight Tully-Fisher Relation • Disks grow in radius in an “onion skin” manner Tully-Fisher falls apart for local low mass galaxies. Local low-mass star-forming galaxies are often not disks .

Outline • Disk Formation “Mass of Disk Formation” o Assembly of disks over cosmic time o • Spheroid Formation Formation timescales vary with galaxy mass and redshift o • JWST observations of nascent galaxies

Gas kinematics tell us about the physical state of galaxies s dominated mixed V rot dominated 6 ” z~1 HST z~1 HST z~1 HST 1 ” 0.75 ” spatial, 8 ” V rot 75 km/s 29 km/s V rot sini = 208 km/s s = 40 km/s 55 km/s 59 km/s

Gas kinematics tell us about the physical state of galaxies s dominated mixed V rot dominated 6 ” z~1 HST z~1 HST z~1 HST 1 ” 0.75 ” σ is a gas velocity dispersion. • Integrates over velocity gradients on scales below the seeing • Quantifies disordered motions in galaxies (Weiner et al. 06, Kassin et al. 2007, Covington, Kassin et al. 2010) • Does not indicate a thick disk like in the Milky Way (Gilmore & Reid 1983)

Tully-Fisher Relation at z~0.2 log stellar mass (M ⦿ ) log V rot (km/s) Kassin et al. 2007

Tully-Fisher Relation from z~0.2 to z~2 z~1 z~0.8 z~2 z~0.2 z~0.5 log stellar mass (M ⦿ ) log V rot (km/s) Kassin et al. 2007; Simons, Kassin et al. 2016

z~1 z~0.8 z~0.2 z~2 z~0.5 log stellar mass (M ⦿ ) log V rot (km/s) log stellar mass (M ⦿ ) 2  0.5V rot 2 + s 2 S 0.5 log S 0.5 (km/s)

Do V rot and σ evolve with time?

The evolution of galaxy kinematics M ★ = 10 10 – 10 11 M  σ V rot 10 9 – 10 10 M  (km/s) (km/s) redshift redshift Representative star-forming galaxies, no cut on morphology Kassin et al. 2012, Simons, Kassin et al. 2017, σ trend also Wisnioski et al. 2015 & Turner et al. 2017

How does the fraction of disk galaxies evolve? Let’s characterize disk galaxies: • V rot / σ ~ 10 (local massive disks) • V rot / σ > 3 (analog of local low mass disks) • V rot / σ > 1 (barely rotation supported) NGC 4388, credit: ESA/Hubble & NASA

V/ σ is correlated with visual morphology V/ σ = 5.6 z=1, Hubble/ACS V+I V/ σ > 3 V/ σ < 3 Disordered V/ σ = 4.9 kinematics & morphology V/ σ = 3.4 V/ σ = 2.5 V/ σ g = 1.8 V/ σ g = 1.6 Ordered kinematics & 6” morphology

Evolution of the fraction of the disk fraction of star-forming galaxies z~1 HST fraction of star- V/ s = 1.6 forming galaxies with V/ σ >1 10 10 – 10 11 M  10 9.5 – 10 10.5 M  10 9 – 10 10 M  redshift Kassin et al. 2012; Simons, Kassin et al. 2016 & 17

Quantitatively, surveys agree fraction of star- forming galaxies with V/ σ >1 10 10 – 10 11 M  10 9.5 – 10 10.5 M  10 9 – 10 10 M  redshift Kassin et al. 2012; Simons, Kassin et al. 2016 & 17

At z~2, most galaxies were not disks z~1 HST Disk Settling Disk Assembly V/ s = 3.4 fraction of star- forming galaxies with V/ σ >3 10 10 – 10 11 M  10 9.5 – 10 10.5 M  10 9 – 10 10 M  redshift Kassin et al. 2012; Simons, Kassin et al. 2016 & 17

Analytic Theory of an isolated disk My observations • Disks start off well-ordered and thin Disks start off with lots of disordered motions. • They thicken with time They lose disordered motions and “thin out” with time. • The Tully-Fisher relation has little scatter Tully-Fisher has large scatter to low rotation velocity. • Disks grow in radius in an “onion skin” manner Disks grow in radius, but not in an orderly manner.

Nbody Shop at U. Washington (courtesy Governato)

Outline • Disk Formation “Mass of Disk Formation” o Assembly of disks over cosmic time o • Spheroid Formation Formation timescales vary with galaxy mass and redshift o • JWST observations of nascent galaxies

How and when do quiescent spheroids form? NGC 1132; credit: Hubble Heritage

How do quiescent spheroids form? • Classical picture that dominated for decades: • Formed in a single burst in the early universe (Partridge & Peebles 1967; Larson 1975) • Mergers of disks can also form an early type (Toomre & Toomre 1972; Toomre 1977) • Breakthrough (Bell et al. 2006, Faber incl. Kassin et al. 2007) : • Quiescent galaxies increase in numbers by a factor of 2-4 over the last 8 billion years since z~1, so all could not have formed in a single burst in the early universe (see also e.g., Faber et al. 1995) • Quiescent spheroids must form from star-forming disks Star-forming galaxies continuously add to the quiescent population, but it’s still unclear how.

What is the path from star- forming disks to quiescent spheroids (“quenching”)? ? NGC 4414, credit: HubbleSite.org NGC 1132; credit: Hubble Heritage