STAR FORMATION HISTORIES OF GALAXIES FROM Z=0-8

Transcription

1 STAR FORMATION HISTORIES OF GALAXIES FROM Z=0-8 Picture Credit: John Davis Peter Behroozi, Stanford University / KIPAC Risa Wechsler and Charlie Conroy

2 Basic Approach

3 Basic Approach

4 Basic Approach Repeat as often as necessary to explore allowable solutions.

5 Basic Approach Data Sets: sat (M peak ) / cen (M) z = 0.1 z = 1.0 z = 2.0 z = 3.0 z = 4.0 z = 5.7 -d 2 N / dz dlog 10 / X(M,z) a = a = a = a = a = Combined Fit Host Mass [M ] O! Weighted Averages Subhalo Merger Mass Ratio [, M peak ] New calibrations of halo mass functions, satellite fractions, and merger rates to z=8 from Bolshoi.

6 Basic Approach Data Sets: Number Density [Mpc -3 dex -1 ] z = 0.1 z = 0.5 z = 1.0 z = 2.0 z = 2.5 z = 4.0 z = 5.0 z = 6.0 z = 7.0 z = Stellar Mass [M O ] Cosmic SFR [M O yr-1 Mpc -3 ] z New Stellar Mass Functions from PRIMUS, others up to z=8 New compilation of csfrs to z=8

7 Basic Approach Data Sets: Specific SFR [yr -1 ] 10-9 Specific SFR [yr -1 ] M * = M O M * = M O z z and SSFRs too!

8 Results Constraints on the M*/Mh ratio, useful for SAMs and hydro: 0.01 M * / z = 0.1 z = 1.0 z = 2.0 z = 3.0 z = 4.0 z = 5.0 z = 6.0 z = 7.0 z = [M O ]

9 Results A clear picture of the star formation history of the Universe: Halo Mass [M O ] Time [Gyr] log 10 (SFR) z

10 Results A clear picture of the star formation history of galaxies: Time [Gyr] Halo Mass [M O ] at z= log 10 (SFR) z

11 Results Low-mass galaxies have had significantly different star formation histories than high-mass galaxies Time [Gyr] (z=0) = M O 1000 (z=0) = M O SFR [M O yr-1 ] (z=0) = M O (z=0) = M O z

12 Results Milky-Way-sized halos have been the most efficient at turning baryons into stars since at least z= Time [Gyr] SFR / Baryon Accretion Rate = M O = M O = M O = M O 10-5 = M O z

13 Results This leaves a clear imprint on the historical conversion ratio: 10 0 Time [Gyr] SFR / Baryon Accretion Rate M O (z=0) M O (z=0) M O (z=0) M O (z=0) M O (z=0) z

14 High-Redshift Histories Constraints on Individual Star Formation Histories 1000 z=3 z=2 z=1 z= z=3 z=2 z=1 z= SF History [M O yr-1 ] = M O SF History [M O yr-1 ] = M O = M O = M O 1 10 Time [Gyr] 1 10 Time [Gyr]

15 High-Redshift Histories Constraints on Individual Star Formation Histories z=3 z=2 z=1 z= SF History [M O! yr-1 ] = M O! SFH = At B SFH = At B exp(-t/ ) SFH = A[(t/ ) B + (t/ ) C ] Time [Gyr]

16 High-Redshift Histories Suggestions that incompleteness is not an enormous problem: Average Galaxy Detection Probability z

17 Mergers and the ICL We can also constrain the buildup of stars from mergers Fraction of Stellar Growth from In Situ Star Formation as opposed to intrinsic star formation: z = 0 z = 0.5 z = 1 z = 2 z = [M ] O

18 10 14 When and Where We can also constrain when and where all stars were formed: z Halo Mass [M O ] log 10 (SFR*ND) Time Since Big Bang [Gyr]

19 10 12 When and Where We can also constrain when and where all stars were formed: z Stellar Mass [M O ] log 10 (SFR*ND) Time Since Big Bang [Gyr]

20 Summary Most of the stars in the Universe were formed in halos similar in size to the Milky Way.

21 Summary Most of the stars in the Universe were formed in halos similar in size to the Milky Way. Unsurprisingly, this is where the gas to stars conversion efficiency also peaks, at about 20-40% of available hydrogen converted into stars.

22 Summary Most of the stars in the Universe were formed in halos similar in size to the Milky Way. Unsurprisingly, this is where the gas to stars conversion efficiency also peaks, at about 20-40% of available hydrogen converted into stars. It s more surprising that this efficiency has remained relatively constant over time!

23 Summary Galaxies in more massive halos initially formed stars efficiently, but then their star formation rates dropped precipitously after z=2-3 (~10 Gyr ago). Galaxies in less massive halos have increasing star formation efficiencies, but fairly flat star formation rates at late times.

24 Summary High-redshift star formation histories are well-approximated by power laws. High-redshift incompleteness may be on the order of 0-20%.

25 Summary At high redshifts, most galaxies build up most of their stars through internal star formation. At late times, massive galaxies switch to mostly merger-driven growth BUT Most mergers in massive halos in fact get disrupted into the ICL, and only a tiny fraction make it to the BCG.

26 Summary Both merger-driven growth and star formation are inefficient at late times in massive halos; it s just that star formation is much *more* inefficient.

27 Thank you for listening!

28 Image Sources John Davis; apod.nasa.gov/ apod/ ap html Azcolvin429; en.wikipedia.org/ wiki/ File:Cosmological_C omposition_- _Pie_Chart.png NASA; en.wikipedia.org/ wiki/ File:CMB_Timeline30 0_no_WMAP.jpg Jesus Vargas; apod.nasa.gov/ apod/ ap html NASA; en.wikipedia.org/ wiki/ File:WMAP_2010.pn g SOHO Consortium; apod.nasa.gov/ apod/ ap html Volker Springel; galform/millennium/ R. Gabany; nature/journal/ v477/n7364/full/ a.html

29 Image Sources Adam Block: apod.nasa.gov/ apod/ ap html HUDF Working Group; apod.nasa.gov/ apod/ ap html NASA; apod.nasa.gov/ apod/ ap html

30 Results Constraints on the M*/Mh ratio, useful for SAMs and hydro: 0.01 M *(z) / (z) z = 0.1 z = 1.0 z = 2.0 z = 3.0 z = 4.0 z = 5.0 z = 6.0 z = 7.0 z = (z=0) [M O ]