TY - JOUR
T1 - Recent star formation in the Hi dominated outer regions of early-type galaxies
AU - Yıldız, Mustafa K.
AU - Serra, Paolo
AU - Peletier, Reynier F.
AU - Oosterloo, Tom A.
AU - Duc, Pierre-Alain
PY - 2016/3
Y1 - 2016/3
N2 - Context According to the ATLAS3D project, about 20 percent of
all nearby early-type galaxies (D <42 Mpc; M K <
-21.5 mag; stellar mass M stars >~ 6 ×
109 M⊙) outside clusters are surrounded by a
disc or ring of low-column-density neutral hydrogen (Hi) gas with
typical radii of tens of kpc, much larger than the stellar body. Aims
Our aim is to understand the impact of these gas systems on the host
galaxies, in particular, whether there is any recent star formation
related to the Hi and effect of recent star formation on the host
early-type galaxies. Methods and sample We analyse the distribution of
star formation out to large radii by using resolved Hi images together
with UV and optical images. We calculate the UV-UV and UV-optical
colours in two apertures, 1-3 and 3-10 R eff. Using FUV
emission as a proxy for star formation, we also estimate the integrated
star formation rate in the outer regions. Our sample consists of 18
Hi-rich galaxies as well as 55 control galaxies where no Hi has been
detected. We select the control sample galaxies to match the Hi-rich
galaxies in stellar mass, environment, distance and stellar kinematics.
Results In half of the Hi-rich galaxies the radial UV profile changes
slope at the position of the Hi radial profile peak. We find that the
FUV-NUV and UV-optical colours in the first and second apertures of the
Hi-rich galaxies are on average 0.5 and 0.8 mag bluer than the Hi-poor
ones, respectively. We also find that the Hi-rich early-type galaxies
have colour gradients that are almost 2 times stronger than the Hi-poor
ones. we estimate the integrated star formation rate in the outer
regions (R > 1 R eff) to be on average ~
6.1×10-3 M⊙ yr-1 for the
Hi-rich galaxies. We find that the gas depletion time in the outermost
region (3-10 R eff) is ~ 80 Gyrs, which is similar to that
estimated for the outskirts of spirals. Conclusions Studying the
stellar populations in early type galaxies with and without Hi, we find
that galaxies with Hi generally show UV and UV-Optical colours in the
outer parts that are bluer than those of early-type galaxies without Hi.
This shows that the Hi is actively involved in recent star formation.
The star formation rate in the outer regions is too low to build a
stellar disc, and therefore change the morphology of the host even when
integrated over several Gyrs. Star formation in outermost regions does
not depend on the type of the galaxies.
AB - Context According to the ATLAS3D project, about 20 percent of
all nearby early-type galaxies (D <42 Mpc; M K <
-21.5 mag; stellar mass M stars >~ 6 ×
109 M⊙) outside clusters are surrounded by a
disc or ring of low-column-density neutral hydrogen (Hi) gas with
typical radii of tens of kpc, much larger than the stellar body. Aims
Our aim is to understand the impact of these gas systems on the host
galaxies, in particular, whether there is any recent star formation
related to the Hi and effect of recent star formation on the host
early-type galaxies. Methods and sample We analyse the distribution of
star formation out to large radii by using resolved Hi images together
with UV and optical images. We calculate the UV-UV and UV-optical
colours in two apertures, 1-3 and 3-10 R eff. Using FUV
emission as a proxy for star formation, we also estimate the integrated
star formation rate in the outer regions. Our sample consists of 18
Hi-rich galaxies as well as 55 control galaxies where no Hi has been
detected. We select the control sample galaxies to match the Hi-rich
galaxies in stellar mass, environment, distance and stellar kinematics.
Results In half of the Hi-rich galaxies the radial UV profile changes
slope at the position of the Hi radial profile peak. We find that the
FUV-NUV and UV-optical colours in the first and second apertures of the
Hi-rich galaxies are on average 0.5 and 0.8 mag bluer than the Hi-poor
ones, respectively. We also find that the Hi-rich early-type galaxies
have colour gradients that are almost 2 times stronger than the Hi-poor
ones. we estimate the integrated star formation rate in the outer
regions (R > 1 R eff) to be on average ~
6.1×10-3 M⊙ yr-1 for the
Hi-rich galaxies. We find that the gas depletion time in the outermost
region (3-10 R eff) is ~ 80 Gyrs, which is similar to that
estimated for the outskirts of spirals. Conclusions Studying the
stellar populations in early type galaxies with and without Hi, we find
that galaxies with Hi generally show UV and UV-Optical colours in the
outer parts that are bluer than those of early-type galaxies without Hi.
This shows that the Hi is actively involved in recent star formation.
The star formation rate in the outer regions is too low to build a
stellar disc, and therefore change the morphology of the host even when
integrated over several Gyrs. Star formation in outermost regions does
not depend on the type of the galaxies.
KW - galaxies: elliptical and lenticular
KW - cD
KW - galaxies: evolution
KW - galaxies: ISM
KW - galaxies: structure
U2 - 10.1017/S1743921316011133
DO - 10.1017/S1743921316011133
M3 - Article
VL - 321
SP - 279
JO - International Astronomical Union Symposium
JF - International Astronomical Union Symposium
SN - 1743-9213
ER -