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Effect of the interactions and environment on optical and radio nuclear activity
Jose Sabater Montes
Institute for Astronomy, University of Edinburgh
with Philip Best (IfA) and Mamen Argudo (IAA Granada)


Introduction


Galaxy interactions and environment play a fundamental role in the evolution of galaxies. Examples of interaction induced evolution:




Star formation. Morphology. Nuclear activity -> quenching of star formation (feedback) -> control of the growth of massive galaxies?

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Galaxy Evolution over Five Decades - Cambridge 2013


Nuclear activity and environment


Effect of environment on AGN is not completely clear yet.
Contradictory results found in the literature. Some open questions:


What is the relative effect of the environment and interactions on
the triggering of an AGN?



Is there a relation between accretion modes (low-excitation or
radio-mode, high-excitation or quasar-mode) and environment?



We present a study that considers:


different aspects of the environment. different types of nuclear activity. the possible effect of galaxy mass as a confounding factor.
Sabater, J., Best, P. and ArgЗdo-FernАndez, M., 2013 MNRAS, 430, 638

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Galaxy Evolution over Five Decades - Cambridge 2013


The sample and the data


Galaxies in the SDSS DR7 spectroscopic survey with redshift between 0.03 and 0.1 (N ~ 268000). Volume limited with Mr - 5log(h) > -20 (N ~ 100000).
Nuclear activity classification:




Optical: using MPA-JHU data ­ Passive, LINER,

Seyfert, Transition Object (TO) and Star Forming.


Radio: from Best & Heckman (2012) ­ radio AGN,

including separation between Low-Excitation and High-Excitation Radio Galaxies (LERGs and HERGs)
05/09/2013 Galaxy Evolution over Five Decades - Cambridge 2013


Environmental parameters


Local density Tidal forces Friends of Friends

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Galaxy Evolution over Five Decades - Cambridge 2013


Environmental parameters


Local density

Tidal forces Friends of Friends
Traces the density of companions around the target galaxy. 10th neighbour
10 10 log Vo l r 10







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Galaxy Evolution over Five Decades - Cambridge 2013


Environmental parameters


Local density Tidal forces

Friends of Friends
Relation between tidal forces exerted by companions and internal binding forces

05/09/2013

Galaxy Evolution over Five Decades - Cambridge 2013


Environmental parameters



Local density Tidal forces Friends of Friends
Estimation of the number of galaxies in the group to which the galaxy belongs From Tago et al. 2010 Galaxies with Mr < -19.2 => reduced sample of ~100000 galaxies
Galaxy Evolution over Five Decades - Cambridge 2013



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Environmental parameters

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Galaxy Evolution over Five Decades - Cambridge 2013


Environmental parameters

"field" isolated

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Galaxy Evolution over Five Decades - Cambridge 2013


Environmental parameters Principal Component Analysis


Remove possible correlations between the parameters. Example: Tidal parameter may be overestimated at higher densities due to the use of projected distances.



05/09/2013

Galaxy Evolution over Five Decades - Cambridge 2013


Environmental parameters Principal Component Analysis


Interpretation:






PCA1 (53%) ­ Overall interaction level PCA2 (31%) ­ One-onone interactions PCA3 (16%) ­ Relative location; high in cluster outskirts and low in locally-compact structures
Galaxy Evolution over Five Decades - Cambridge 2013

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Effect of the mass


Known relation between mass and AGN prevalence (Best et al. 2005; Kauffmann et al. 2003). Prevalence of AGN with respect to environmental parameters may be biased by the mass distribution.



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Galaxy Evolution over Five Decades - Cambridge 2013


Effect of the mass


Mass slices ­ optical and radio AGN

overall interaction

one-on-one interaction

relative location

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Galaxy Evolution over Five Decades - Cambridge 2013


Stratified study


Stratifed study that considers several strata of mass. Cochrane-Mantel-Haenzsel (CMH) test used in medical studies...




Patients Exposure to risk factor Incidence of disease
Galaxy Evolution over Five Decades - Cambridge 2013

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Stratified study


Stratifed study that considers several strata of mass. Cochrane-Mantel-Haenzsel (CMH) test applied to astronomy:




Galaxies Exposure to environmental factor Incidence of nuclear activity
Galaxy Evolution over Five Decades - Cambridge 2013

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Stratified study


CMH odd ratios (~ relation between prevalences)

overall interaction

one-on-one interaction

relative location

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Galaxy Evolution over Five Decades - Cambridge 2013


Results of the stratified study
Density; FoF; overall interaction level (PCA1): Opposite trends for optical and radio AGN.

overall interaction

one-on-one interaction

relative location

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Galaxy Evolution over Five Decades - Cambridge 2013


Results of the stratified study
One-on-one interactions (PCA2). Time delay in the setting of different types of optical activity? (e.g. Wild et al. 2010)

overall interaction

one-on-one interaction

relative location

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Galaxy Evolution over Five Decades - Cambridge 2013


Results of the stratified study


LERG vs. HERG: HERG significantly more similar to optical AGN than to LERG with respect to the density parameter.

overall interaction

one-on-one interaction

relative location

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Galaxy Evolution over Five Decades - Cambridge 2013


Results of the stratified study


LERG vs. HERG and optical AGN: Warm versus cold gas accretion.
warm

cold
overall interaction one-on-one interaction relative location

05/09/2013

Galaxy Evolution over Five Decades - Cambridge 2013


Results of the stratified study


LERG vs. HERG and optical AGN: Warm versus cold gas accretion but...

overall interaction

one-on-one interaction

relative location

05/09/2013

Galaxy Evolution over Five Decades - Cambridge 2013


Results of the stratified study
Triggering of LERG is also related to one-on-one interactions (PCA2), like optical AGN.

overall interaction

one-on-one interaction

relative location

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Galaxy Evolution over Five Decades - Cambridge 2013


Results of the stratified study
Triggering of LERG is also related to one-on-one interactions (PCA2), like optical AGN. Chaotic cool accretion (Gaspari+ 2013)?

overall interaction

one-on-one interaction

relative location

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Galaxy Evolution over Five Decades - Cambridge 2013


Conclusions


Decrease of optical AGN and increase of radio AGN prevalence towards denser environments. Probably explained by the presence/absence of a supply of cold gas. The relation of HERGs with density is similar to that of optical AGN and different to that of LERGs. One-on-one interactions triggers both optical and radio nuclear activity. Hence, accretion by the cooling of warm gas is not the only mechanism related to the triggering of LERGs.
Sabater, J., Best, P. and ArgЗdo-FernАndez, M., 2013 MNRAS, 430, 638





05/09/2013

Galaxy Evolution over Five Decades - Cambridge 2013