The global star formation laws in galaxies recent updates
This presentation is the property of its rightful owner.
Sponsored Links
1 / 32

The Global Star Formation Laws in Galaxies: Recent Updates PowerPoint PPT Presentation


  • 68 Views
  • Uploaded on
  • Presentation posted in: General

The Global Star Formation Laws in Galaxies: Recent Updates. Yu Gao Purple Mountain Observatory Chinese Academy of Sciences . May 15, 2012 @5 th sino-french. Outline of this talk.

Download Presentation

The Global Star Formation Laws in Galaxies: Recent Updates

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


The global star formation laws in galaxies recent updates

The Global Star Formation Laws in Galaxies: Recent Updates

Yu Gao

Purple Mountain Observatory

Chinese Academy of Sciences

May 15, 2012 @5th sino-french


Outline of this talk

Outline of this talk

  • What are the star formation (SF) recipes? SFR-gas (HI, CO) scaling laws: Kennicutt - Schmidt law, SF laws in other forms

  • Why do we need a SFR-dense gas law

  • A linear FIR(SFR)--HCN (dense gas tracer) relation for all star-forming systems (GMCs-->high-z): SF law indense gas

  • Major issues and debates (CS surveys)

  • Conclusions


Star f ormation laws

Star formation laws

  • Schmidt (1959): SFR~density(HI)^n,

    n=1-3, mostly 2-3 in ISM of our Galaxy.

  • Kennicutt (1989):

    Disk-average [SFR~ density(HI+H2)^n]

    n is not well constrained. ~1-3, wide spread.

  • Kennicutt (1998): n=1.4 ?

    Total gas (HI + H2) vs. Dense gas

  • Better SF law in dense gas?

    (Hubble law and H0analogy)


Hubble law

Hubble law


The global star formation laws in galaxies recent updates

Kennicutt

1998

n=1.4


The global star formation laws in galaxies recent updates

IR circumnuclear starbursts

Normal disk spirals


The global star formation laws in galaxies recent updates

SFR vs. M(H2): No Unique Slope:1, 1.4, 1.7?

H2-dominated

LIRGs/ULIRGs

HI ~ H2

HI-dominated

LSB galaxies

Extragalactic SF=CO until 90’s

Gao & Solomon 2004b ApJ


The global star formation laws in galaxies recent updates

SF thresholds may

simply reflect the

change of the

dominant cold gas phase in galaxies

from HI ->H2 & from H2->denseH2

Bigiel’s talk @SFR50

Schruba+2011

~linear in H2!


The global star formation laws in galaxies recent updates

GMCsenbed in diffuse atomic gas(HI), the gas reservoir for

molecular clouds,

and the supply for future star formation.

PDRs


The global star formation laws in galaxies recent updates

Stars are forming in giant molecular clouds (GMCs)


The global star formation laws in galaxies recent updates

High DensityTracersMerging/interactions trigger gasinfall to nuclearregionsNucleiof Galaxies shouldpossessdensergasas GMCs have to survive to tidal forces (must bedenser)

Criticaldensity: the radiating molecule (eg, CO) suffers

collisions at the rate: n(H2) sigma v = A

(Einstein coefficient A ~ nu^3 mu^2)

* High-J(>~3)levels of CO (nu ~ J)

highercriticaldensity to beexcited (>105cm-3)

* & High dipole moment molecules

HCN, HNC, HCO+, CS (mu ~ 30x > CO), etc..

* X factor ? CO-to-H2, HCN-to-DenseH2 conversions


The global star formation laws in galaxies recent updates

Dense gas is the essential fuel for high mass star formation in galaxies

HCN Surveys in 53 Galaxies: Gao & Solomon 2004a ApJS

Far-IR, HCN, CO Correlations: Gao & Solomon 2004b ApJ


The global star formation laws in galaxies recent updates

SFR

Dense Molecular Gas


The global star formation laws in galaxies recent updates

Baan, Henkel, Loenen + 2008

HCN,CS,HNC etc. in SF gals.

  • Baan et al. (2008)

  • Kohno 2007, et al. (2003)

  • Imanishi (2006)

  • Aalto et al. 2007, 2002, 1995

  • Solomon et al. 1992

  • Nguyen et al. 1992

  • Henkel et al. 1990

  • Henkel, Baan, Mauersberger 1991

Best case studies: Arp 220 & NGC 6240 (Greve + 2009)


The global star formation laws in galaxies recent updates

Gao, Carilli, Solomon & Vanden Bout 2007 ApJ, 660, L93

13 HCN @high-z


The global star formation laws in galaxies recent updates

Fit to Galaxies

Wu, Evans, Gao

et al. 2005 ApJL

Fit to GMCs

Wu+2010

Fit to both

GMCs & Gals..


The global star formation laws in galaxies recent updates

CARMA+45m CO (Koda + 09)

HST


The global star formation laws in galaxies recent updates

  • Total useful on-source integration time >~110 hours.

  • HCN spectra with S/N>3

    (a channel width dV ~7 km/s).

  • Typical rms ~1-2 mKat dV~20 km/s.


The global star formation laws in galaxies recent updates

HCN contours

are overlaid on

the CO image


The global star formation laws in galaxies recent updates

SFR

  • Correlations between 8um-HCN & 24um-HCN. The solid lines: fixed slope of 1.

HCN


The global star formation laws in galaxies recent updates

M33GMCs (Rosolowsky, Pineda & Gao 2011)

Chen & Gao in prep.


The global star formation laws in galaxies recent updates

∑Mdense vs. ∑SFR

Liu & Gao arXiv:1106.2813

Dense H2 show the best correlation with SFR (linear Liu & Gao 2011).


The global star formation laws in galaxies recent updates

K-S SF Law in high-redshift galaxies

Daddi et al. 2010; Genzel+2010

Two major SF modes:1. a long-lasting mode for disks (local spirals and BzKs)

2. a rapid starburst for LIRGs ULIRGs & SMGs/QSOs

CO->H2 conversion factor

?? αco (Msun (K km/s pc2)-1:

4.6 for local spirals

3.6 ± 0.8 for BzKs

0.8 for LIRGs/SMGs/QSOs


The global star formation laws in galaxies recent updates

Bi-modal SF laws in high-z gals (Daddi+2010; Genzel+2010) also exist in local gals


The global star formation laws in galaxies recent updates

Juneau+2009; Narayanan+2008; Krumholz & Thompson 2007; Iono+2008; Mao+2010

SFR – CO & SFR -- HCN indexes


The global star formation laws in galaxies recent updates

  • Dense gas over a range of 10^4-8 /cm^3


Concluding remarks

Concluding Remarks

  • SF: quiescent (few Dense Cores=DCs), normal, active/burst modes (starbursts: active formation ofDCs)

  • DCsin Dense Molecular Gas Complexes  High Mass Stars/Clusters (SF in different environments: SMGs/hi-zQSOs; ULIRGs/Starbursts; Spirals; LSBs;DCs)

  • SF thresholds: change of the dominant cold gas phase in galaxies from HI ->H2 & from H2->denseH2

  • (FIR-HCN, CS Linear Correlations) SFR ~ M(DenseH2): the total mass of dense molecular gas in galaxies & all star-forming systems (spanning 10 orders of mag.)?

  • SFR-DenseGas: Counting DCs(=SF units) in Galaxies?

Gao & Solomon: Dense H2DCs/StarsClusters


New star formation law

New Star Formation Law

  • Dense Molecular Gas  High Mass Stars

  • SFR ~ M(DENSE) ~ density of dense gas

    (e.g. gas density >~10^5 cc), linear

  • HI  H2 DENSE H2 Stars

Schmidt law : HI  Stars

Kennicutt : HI + H2 Stars

Gao & Solomon: Dense H2 Stars

From Cores to High-z: Dense GasMassive SF


  • Login