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Neutral Hydrogen and Star Formation in the Coma-A1367 Supercluster.

Luca Cortese School of Physics & Astronomy ­ Cardiff University


Outline of the Project
GOAL: Gain additional insights on the mechanisms and timescales which regulates the
migration of galaxies (L>109 L ) from the blue to the red sequence by combining UV and HI.

Adapted from Boselli, Boissier, LC, Gavazzi, 2008, ApJ, in press


Outline of the Project
GOAL: Gain additional insights on the mechanisms and timescales which regulates the
migration of galaxies (L>109 L ) from the blue to the red sequence by combining UV and HI. Volume limited sample (~90-100 Mpc from us) including galaxies in different environments.

SKY REGION: Coma-Abell1367 supercluster.

Coma A1367

Coma

A1367

First step: the 2 clusters and their outskirts. In particular: A1367: HI selected sample -- 5x1 deg2 ­ part o
AGES survey
(LC et al. 2008a, MNRAS, 383, 1519)

DATASET: UV+HI+Opt.

f the

COMA: UV selected sample ­ ~3x3 deg2 ­
GALEX
(LC et al. 2008c in prep.)

GI1


AGES-A1367 field
Mass limit ~ 6x108 M for W~200 km/s
(at the distance of A1367: ~93 Mpc)

54 in the A1367 volume (4000 (100 HI sources, 79 new(!) in the whole AGES volume: 0
HI galaxies show a Large Scale Distribution different from optically selected galaxies. Healthy spirals not yet infalled into the cluster?
LC et al. 2008a, MNRAS, 383, 1519

AGES dataset publicly available at http://www.naic.edu/~ages/public_data.html


Colour-Magnitude distribution in the AGES-A1367 sample

OPTICAL g-i COLOUR i MAGNITUDE RELATION

FUV-i COLOUR i MAGNITUDE RELATION

All HI galaxies lie in the blue sequence in a UV-optical CM diagram. However not all blue sequence galaxies are detected in HI: ~15-20% of galaxies in the blue sequence are HI deficient.


Blue HI poor galaxies

All these objects are still forming stars (e.g. detected in H), but they show recent SF only in the inner part of their disk. In the outer parts of the stellar disk, SF has already ended.

All within 1 deg from the cluster centre: environmental effects?


Transition Galaxies
Progeny of the blue HI deficient objects?

In less than 1 Gyr these objects will migrate (at least) towards the transition region between the blue and the red sequence.

The few A1367 galaxies in the transition region are in fact cluster spirals with low residual SF activity
(But more statistic needed)


Can we test this scenario elsewhere?
Coma: no blind HI data yet, but wide UV coverage and SDSS spectroscopy! We can start looking into the properties of galaxies in the transition region. NGC4921 Brightest Spiral in Coma
(e.g. Bravo-Alfaro et al. 2001)

well known HI deficient-ram pressure stripped galaxy

Transition galaxies have strong Balmer lines in absorption: quenched SF?


Can we test this scenario elsewhere?
Coma: no blind HI data yet, but wide UV coverage and SDSS spectroscopy! We can start looking into the properties of galaxies in the transition region. NGC4921 Brightest Spiral in Coma
(e.g. Bravo-Alfaro et al. 2001)

well known HI deficient-ram pressure stripped galaxy

Transition galaxies have strong Balmer lines in absorption: quenched SF?

By combining HI and UV data we can select galaxies at different stages of their transition between the blue and the red sequence! From Healthy Spirals to HI blue deficient and transition galaxies.


UV dust correction is not straightforward!
All methods calibrated on TIR/FUV vs. A(FUV) relation for starburst galaxies :
(e.g. Gordon et al. 2000, Buat et al. 2005)

But...the TIR/FUV vs. A(FUV) depends strongly from the specific SFR!!!
(e.g. Kong et al. 2004)

b>1 b~0.5

b~0.06

b~0.02 b<0.01

Using the TIR/FUV vs. A(FUV) calibrated on SF galaxies we systematically overestimate A(FUV) by up to 1-2 mag for transition objects!

LC et al. 2008b, MNRAS, submitted


Summary
In HI the large scale structure is significantly different than in optical. HI+UV+optical = powerful tool for selection galaxies at different stages of their evolution. A correct estimate of UV dust attenuation is crucial for the interpretation of the UV-opt CM diagram.


The future
Short time-scale Increase the size of our sample and compare the properties of galaxies in different environments. Quantify the timescales of the transformation by combining data and models. Long time-scale Include other ISM components playing a role in the star forming cycle: e.g. dust. In ~1 year study dust will become possible thanks to Herschel (100-600 m: i.e. ALL the dust SED): Synergies between Herschel and current/future HI projects: step forwards in understanding galaxy evolution. The Herschel Reference Survey (P.I. Boselli/Eales). Guaranteed Time. Volume limited optically selected sample (15

The Herschel Virgo Cluster Survey (P.I. J.Davies). OT Key Project accepted. Blind survey of 60 deg2 in Virgo at 110,170, 250, 350, 500 m. (M(dust)>104 M).


The Herschel ~600 Degree Survey (P.I. S.Eales). OT Key Project accepted. Blind survey of ~600 deg2 at 110,170, 250, 350, 500 m. (M(dust)> 104.5 M).