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Bar Parameter Evolution
over the Last 7 Gyr
Isabel Pérez,
Universidad de Granada, UGR
J.A.L. Aguerri (Instituto de Astrofísica de
Canarias, IAC)
J. Méndez-Abreu (IAC)
Dynamics of Disk Galaxies, October 2013, Seoul, Korea
Stellar bars contribute only 1020% of the disc mass. Efficient
at
redistributing
angular
momentum and mass.
Bar formation and destruction
rate as well as the
morphological and dynamical
changes are affected by the
angular momentum exchange.
Cosmological evolution of bar
fraction can depend on this
effect.
Bar fraction

Observations show that bars are ubiquitous ~45% optical, up
to 70% NIR (e.g. Optical: e.g. Marinova & Jogee 2007; Aguerri
et al. 2009; Masters et al. 2011; NIR: e.g. Eskridge et al. 2000;
Menendez-Delmestre et al. 2007)

Bar fraction depends on morphological type being lower in
lenticular galaxies than spirals (e.g. Marinova & Jogee 2007;
Méndez-Abreu et al. 2010).

Bar fraction is correlated with galaxy mass (Méndez-Abreu et
al. 2010; Nair & Abraham 2010) and colour (Hoyle et al. 2011)

It does not seem to be strongly affected by environment (e.g.
Aguerri et al. 2009)
Bar fraction

The evolution of the bar fraction with redshift.
The bar fraction at z~0.84 is one-third of the present-day
value (e.g. Sheth et al. 2008, Melvin et al 2013)
 ʻDonwsizingʼ of bar fraction (Sheth et al. 2012)
Bars have been common structural components of
the disc of galaxies during the last 8 Gyr.
Bars are fully characterised by three observational
parameters: Length, strength and pattern speed
Bar length, strength and pattern
speed
Bar pattern speed, Ωbar:
Main kinematic observable, describes the dynamics of the bar.
It is parametrised by a distance-independent parameter
ℜ=RCR/Rbar
Bars that end near corotation ( 1< ℜ<1.4) are considered to be
fast; while shorter bars are called slow.
Direct methods to determine the pattern speed:
 Tremaine & Weinberg method (1984) using a set of kinematic
measurements to derive Ωbar , requires high S/N data (e.g.
Merrifield & Kuijken 1995; Aguerri et al. 2003; Aguerri et al. ,CALIFA New
Results submitted, 2013)
speed
Indirect methods to determine the pattern speed:

Bar pattern derivation based on numerical models (matching to
velocity fields: e.g Weiner et al. 2001; Pérez et al. 2004; matching to
galaxy morphology: Hunter et al. 1988; Laine et al. 1998; Aguerri et al.
2001)

Identifying morphological or kinematic features with
resonances (shape of dust lanes; Athanassoula 1992; phase shift
J. Beckman, this conference). Connecting the location of the rings
to orbital resonances; Buta 1986).
Connecting the location of the rings to
orbital resonances
 Introduced by Buta 1986, based on theoretical work by Schwarz
(1981,1984)
Connecting the location of the rings to
orbital resonances
OLR
The rate of rotation
of the bar or
pattern speed
determines the
position of the
resonances.
Corotation
ILR
The angular frequency of circular motion and Ωc = Ω ± k/2
Buta et al 1998
Pattern speed with redshift
We study observationaly for the first time the change of these parameters
with redshift, going from the local Universe to z~0.8 (Pérez, Aguerri,
Méndez-Abreu 2012 A&A)
1) Low-redshift sample:
18 barred ringed galaxies SDSS (from
Aguerri et al. 2009) ; 0.01<z<0.01,
inclination < 40deg.
1) High-redshift sample:
26 barred ringed galaxies
COSMOS/ACS; 0.125<z<0.75
(zCOSMOS; Lilly et al. 2007),
inclination < 40deg. F814W filter
Shortest bars we can resolve are for SDSS 0.5 - 2 kpc (z~0.01 - 0.04) and
for COSMOS 0.6 - 2.2 kpc (z~0.125 -0.8)
•Ring Clasification from
Buta & Crocker 1991
• Intrinsic ellipticity varies
from the R1; ~0.74 +0.08 to the R2; ~0.87 +0.08 (Buta et al. 1995)
• We only kept R2 types
since they are
intrinsically rounder, very
similar to that of typical
dics (Fasano et al. 1993;
Ryden 2004)
Bar Length measured as the midpoint between the radius of maximum
and minimum ellipticity, representing the extreme cases for bar
measurements (Michel-Dansac & Wozniak 2006)
Ring radius, in this region the ellipticity and the PA remain constant
Results
 The mean bar radius of our low- and high- redshift samples
are 4.5±1.04 and 3.5±1.33. Both samples have similar bars
and also similar to local samples.

The bar size range covers 2.5 to 6.3 kpc. Most bars in the
local Universe (about 70%) are within this bar-size range

Both samples cover the same range of bar strengths. The
mean value of our low- and high- redshift samples are
0.20±0.07 and 0.17±0.05. Similar to the mean strengths of
bars in the local Universe (0.20±0.07; Aguerri et al. 2009)
All bars are compatible with being ʻfastʼ ( 1< ℜ<1.4)
Possible caveats




Inclination: no influence of the inclination on the ratio with redshift.
Are ring galaxies biased towards a particular pattern speed? resonant
outer rings can be present at different pattern speeds (e.g. Byrd et al.
1994)
No bar size significant difference using r- and g-band (Gadotti 2011)
Completeness of the sample? Only 30% of the local bars show longer
lengths (Aguerri et al. 2009). Studies of high-z bars (e.g. MenendezDelmestre et al. 2007) show that bar size is similar to local galaxies.
30% upper limit to the bars suffering a change in their pattern speed
in the last 7 Gyr.
The remaining 70% of bars did not substantially lose angular
momentum to the halo.
Question remains for very late-type galaxies, gaseous rich spirals
No evolution or bars being short-lived? Simulations show gas-rich
bars are short-lived (e.g. Bournaud & Combes 2002) with life-times of
1-2 Gyr. But our bars are typical of early type spirals and
observational evidence suggest that early type bars are long-lived
(Pérez et al. 2009, Sánchez-Blázquez et al. 2011)
Our result imply that bars do not grow significantly in size with time
Pattern speed vs morphology: new
results from the CALIFA survey
CALIFA: Calar Alto Legacy Integral Field
Area Survey
Legacy Survey of Galaxies in the Local Universe,
using Integral Field Spectroscopy
(Sánchez et al. 2012, Huseman et al. 2013)
PI: S.F.Sánchez, IAA
• ~600 galaxies in the local universe
• 250 observing nights with the PMAS/PPAK integral field
spectrophotometer, on the Calar Alto 3.5 m telescope
• 82 members of 13 countries (25 institutes)
• Started on July 1st 2010.
B. Jungwiert´s talk on Thursday
Aguerri et al. Submitted 2013
Compatible with fast bars
 No significant trend with morphology

Aguerri et al. Submitted 2013
Summary and conclusions
 We have analysed 44 low-inclination ring barred galaxies,
0<z<0.8 to study the evolution of the pattern speed in the last
7Gyr.
 We find that the bar pattern speed does not change with z
 All the studied bars are compatible with fast rotators
 If the bars analysed are long-lasting their size and bar
strength has not significantly changed with time
Implications for the dark halo concentration. Dark matter
does not dominate the potential in the inner regions
speed
Bar length:





Visual inspection: (e.g. Kormendy 1979; Martin 1995; Méndez-Abreu et al.
2010, Edmond Cheung et al. this conference)
Maximum ellipticity (e.g Wozniak et al 1995; Laine et al. 2002)
Variations of the isophotal angle (e.g Sheth et al. 2003)
Fourier moments (e.g Quillen et al. 1994; Aguerri et al. 2000,2003)
Photometric decomposition of profiles (e.g. Prieto et al. 1997; Aguerri et
al. 2005; Laurikainen et al. 2005)
The resulting studies report a typical bar length about 3-4 Kpc; and it
strongly correlates with the disc scale-length (e.g. Aguerri et al. 2005;
Pérez et al. 2005; Erwin 2005)
speed
Bar strength:



Bar torques (Buta & Block 2001)
Isophotal ellipticity (e.g Martinet & Friedli 1997; Aguerri 1999)
Fourier modes (e.g. Ohta et al. 1990; Athanassoula & Misiriotis 2002)
This parameter depends on galaxy morphology. Bars in
lenticulars are weaker than in spirals

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