RemoveYoung (RY) A tool for the removal of the young stellar - - PowerPoint PPT Presentation

RemoveYoung (RY)

A tool for the removal of the young stellar component within an adjustable age cutoff

(based on Gomes & Papaderos 2016, A&A, 594, A49)

Polychronis Papaderos and Jean Michel Gomes

Institute of Astrophysics and Space Sciences (IA)

a tiny mass fraction of young (low M/L ratio) stars can dominate the light (optical morphology) and overshine faint structural/morphological features in the underlying old stellar component

• f a galaxy (for example, relics from minor mergers)

→ the stellar surface density Σ (M⊙/pc2) is in some respects a more useful & robust quantity than the optical/NIR surface brightness μ (mag/arcsec2) … however, Σ is not an observable ... μ (mag/arcsec2) can strikingly differ from Σ … but the latter (more specifically, the intrinsic stellar mass density ρ (M⊙/pc3) determines, together with ρ(gas+DM) ) the gravitational potential of a galaxy

Starburst99 (Leitherer et al. 1999)

Instantaneous SF model (Salpeter IMF & solar metallicity)

3 mag

Motivation

Techniques for 2D determination of Σ (… which is dominated by older (higher M/L) stars)

near-infrared imaging … but i) nebular continuum can be important in starburst galaxies

C

• n

t r i b u t i

• n
• f

n e b u l a r e m i s s i

• n

i n i n d i v i d u a l fj l t e r s

Krüger et al. (1995)

Near IR b: burst parameter = M✶(starburst)/M✶

Techniques for 2D determination of Σ

ii) NIR imaging does not permit to isolate the luminosity output from stars older than a user-defined cutoff (e.g. with t > 108 yr)

Noeske et al. (2003)

Techniques for 2D determination of Σ

The young & intermediate-age stellar component contributes significantly to the emission in the NIR J, H and Ks (~1-2.2 μm) bands with optical/NIR photometry it is impossible to isolate the emission of stars younger than a certain age (for example, exclude pre-AGB stars with an age <108 yr)

Conroy (2014)

NIR

Techniques for 2D determination of Σ

Wuyts et al. (2012): SED fitting using 7 HST bands (ACS + near-IR WFC3)

determination of Σ by spaxel-by-spaxel SED fitting (e.g. Wuyts+12) … this approach does not permit to strip off galaxy images from stars younger than

an adjustable cutoff tcut

Cases where bi-dimensional subtraction of the light contribution from stars

younger than an adjustable cutoff tcut could add further insights into the assembly history of galaxies … (?) Examples: Propagation of star-forming activity in interacting/merging systems like the Antennae, or low-mass starburst galaxies near and far, such as blue compact dwarf (BCD) galaxies, green peas (GPs) and tidal dwarf galaxies (TDGs) :: Subtraction of stellar populations with an age t1 … N offers a means to study a) how SF is synchronized on galactic scales and b) SF propagation effects (incl. estimates of the SF propagation velocity) Subtraction of the starburst component → study of the underlying galaxy host in BCDs Galaxies in galaxy clusters: initial SF episode, ram pressure stripping & galaxy harassment Assembly history of massive early-type galaxies: how has μ(R) and Σ evolved over, say, the past 9 Gyr (since z~1.4)?

Motivation behind the development of RemoveYoung

BCDs: Profile decomposition into the SF component and the underlying host (with the goal of determining μ and Σ for the host galaxy)

Papaderos et al. (2002) plateau P25, E25: isophotal radius of the star-forming and LSB component line-of-sight intensity contribution of the SF component: ~40% at P25, 4% at E25

SBS 0335-052: HI cloud with a projected size of 70×20 kpc; mass of ~109 M⊙

The pair of young BCD galaxy candidates SBS 0335-052 E&W

(see discussion in Pairwise galaxy formation and galaxy downsizing; Papaderos 2012)

Pustilnik et al. (2001)

• Study of the V-I color and spatial

distribution of stellar clusters using HST data →

• galaxy is forming in a propagating mode

from northwest to southeast with a mean velocityof ~20 km/s. 7

Slit1

Papaderos et al. (1998)

SBS 0335-052E: formation through SF propagation

HST/WFPC2, I band, unsharp masked HST/WFPC2, V band

Starburst activity in BCDs

Henize 2-10

Nearby (D=8.7 Mpc) BCD Starburst since 107 yr (Conti & Vacca 1996,

Papaderos & Fricke 1998)

Wolf-Rayet features Young Stellar Clusters (YSCs) a) diffuse component of low-mass YSCs (≃103 M⊙) b) compact & massive YSCs “Super-Star Clusters” (SSCs) 60 pc

Super-Star Clusters

Papaderos et al. (2006)

Henize 2-10: Hα supershells and large-scale gas outflows

b) bipolar outflow of hot and metal-enriched gas from the starburst component,

expanding with velocities of ≥200 km s-1 into the ambient interstellar medium.

a) mechanical luminosity for a Star Formation Rate of 1 M⊙ yr-1 as a function of time

Luminosity Power at t=107 yr : 4×1041 erg s-1 (total energy injected into the ISM: 4.5×1055 erg) H equivalent width map

Papaderos & Fricke (1998)

a) b)

Papaderos & Fricke (1998)

ROSAT HRI X-ray map

Östlin et al. (2003) 2.6 kpc ESO 338-IG04

Lagos et al. (2011)

N e a r l y c

• e

v a l s t a r f

• r

m a t i

• n
• n

s p a t i a l s c a l e s

• f

. 2

• .

5 k p c

Synchronization & propagation of SF activities in blue compact galaxies

TDGs: low-mass self-gravitating entities forming out of tidally ejected matter in interacting/merging galaxy pairs

Tidal Dwarf Galaxies:

does gas collapse within a gravitational potential formed by tidally ejected stars?

Duc et al. (1997) Barnes & Hernquist (1996)

SFH of galaxies in galaxy clusters

Poggianti et al. (1999) Chung et al. (2009) Sun et al. (2010)

IC 3418 in the Virgo Cluster

Hester et al. (2010)

Quilis et al. (2000)

RemoveYoung a post-processing tool for Spectral Population Synthesis (SPS) models

SPS fit with STARLIGHT (Cid Fernandes et al. 2005): Decomposition of a galaxy spectrum into simpe stellar populations (SSPs: instantaneously formed stellar populations, fully characterized by their age, metallicity and IMF)

Sánchez-Janssen et al. (2013)

Secondary quantities, e.g. mass and luminosity-weighted stellar age

The idea behind RemoveYoung (RY)

i) Process spaxel-by-spaxel integral field spectroscopy (IFS) data of a galaxy in order to obtain its spatially resolved star formation history (SFH), which is encoded in the best fitting population vector PV (mass fraction (%) of simple stellar populations- SSPs of a given age and metallicity) ii) reconstruct the (UV-through-NIR) spectrum of the galaxy at each spaxel from the PV after removal of SSPs younger than an adjustable age cutoff tcut & convolve the synthetic SED with a set of filter transmission curves to obtain the 2D surface brightness distribution μ(x,y,band) of a galaxy after suppression of emission from stars younger than tcut (example: compute a synthetic SDSS g-band image for a galaxy

after removal of stars younger than 100 Myr)

iii) additionally, compute from the PV the Σ of stars older (or younger) than tcut →

reconstruct in 2D the mass assembly history of the galaxy since tcut (t1 < tcut < tN )

left: SDSS spectrum of a galaxy as observed (orange & spectral fit in light-blue) and

after application of RY for a tcut of 30 Myr (dark blue), 0.5 Gyr (green) and 5 Gyr (red) SDSS filter transmission curves shown as shaded areas

Application of RemoveYoung to single spectra

Gomes & Papaderos (2016)

Application of RY to integral field spectroscopy data

Gomes & Papaderos (2016)

RemoveYoung: Studies of the structural properties of the underlying host galaxy in BCDs

Gomes & Papaderos (2016)

RemoveYoung (Gomes & Papaderos 2016) is a new spectral population synthesis

post-processing tool that permits reconstruction of the SED and stellar mass M after subtraction of stars older than an adjustable age cutoff tcut

Simple extension of RY from 1D to 2D: spaxel-by-spaxel post-processing of PVs

for IFS data modeled with a spectral population synthesis code (e.g. Starlight, Steckmap, FADO)

→ 2D determination of Σ and the UV-NIR morphology μ(x,y) of a galaxy in various (currently ~ 20) photometric bands RY is a powerful new tool with significant potential of advancing our

understanding on the assembly history of galaxies – from BCDs to ETGs

(!): 2D applications of RY should include a critical consideration of (but could

also help better understanding) effects of e.g. stellar diffusion/migration and a possible non-universality of the IMF in galaxies.

Summary

Application of RemoveYoung on single spectra

(check www.spectralsynthesis.org and www.iastro.pt for updates)