Observations of the Intra-Cluster Light Magda Arnaboldi, European - - PowerPoint PPT Presentation

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Observations of the Intra-Cluster Light Magda Arnaboldi, European Southern Observatory , Garching M. Arnaboldi Observations of the ICL MPIA, July 2 2018 1 Observations of the Intra-Cluster Light Outline 1.

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

Observations of the Intra-Cluster Light

Magda Arnaboldi, European Southern Observatory , Garching

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018
  • 1. Observations of ICL in clusters – A review
  • 2. ICL from deep photometry
  • 3. Observational obstacles
  • 4. Brightest Cluster Galaxies and ICL in clusters
  • 5. Specific energies: using planetary nebulae as

tracers of light components

  • 6. Conclusions

Outline

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Many thanks to collaborators A. Longobardi, J. Hartke, C. Pulsoni, O. Gerhard, K. Freeman,

  • S. Okamura & L. Coccato, J.A.L. Aguerri, C. Barbosa, R. Ciardullo, K. Dolag, J.J. Feldmeier,

G.H. Jacoby, J. C Mihos, G. M. Murante, N.R. Napolitano, N. Castro-Rodriguez, G. Ventimiglia.

Observations of the Intra-Cluster Light

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The Age of Heroes (1951 – 1988)

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Credit: J.J. Feldmeier

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The Age of Heroes (1951 – 1988)

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Credit: J.J. Feldmeier

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The Age of Heroes (1951 – 1988)

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Credit: J.J. Feldmeier

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The early CCD era (1989 – 1998)

Struble (1988) – A 545 Davies et al. (1989) – A1367 Uson et al. (1991a; 1991b) – A2029, 910, 1413, 1763, 2218 Scheick et al. (1994) – A2670 Vilchez-Gomez (1994) – A2390, Cl 1613+31 Tyson et al. (1995; 1998) – A1689, Cl 0024+1654 Boughn et al. (1997) – A115, 403, 2397 Abell 2029 (Uson et al. 1991)

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Credit: J.J. Feldmeier

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ICL from deep photometry

  • Core of the Coma cluster:

Photographic photometry Thuan & Kormendy 1977

  • Abell 4010 (left, z=0.096)

Abell 3888 (center, z=0.151) Deep CCD photometry Krick & Bernstein 2007 Abell 1914 (right) Feldmeier+2004

See also Melnick+’77, Bernstein ’95, Feldmeier+’04, Gonzalez+’05, Mihos+’05, Krick+’06 7

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018
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ICL from deep photometry cont.

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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SDSS with stacking methods (Zibetti et al. 2005) Local Universe in the Virgo (Mihos et al. 2005, 2017) , Fornax (Iodice et al. 2016, 2017), Hydra cluster (Arnaboldi et al. 2012), Dragonfly (Merritt, Abraham +), NGC 6166 in ABELL 2199 (Bender et al. 2015)

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ICL from deep photometry cont.

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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HST at intermediate redshifts in the Frontier Field and CLASH (Montes & Trujillo 2014, 2015; DeMaio + 2015, Burke+2015, Morishita+2017) HSC at intermediate redshifts (Huang et al. 2017)

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ICL properties in individual clusters

  • ICL surface brightness profile shape

varies between clusters - Krick & Bernstein+07 & Huang+17

  • Ellipticity generally increases with

radius, position angle sometimes has sharp variations - Gonzalez+05 & Huang+17

  • Suggests ICL is dynamically young

and separate from BCG

1 10 100 (kpc/h) PA (o) 50

  • 50

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

ICL fraction in individual clusters varies:

~4-21% (in B, Krick & Bernstein 2007) ~10-30% (Feldmeier+’04) ~5% in Virgo, isolated regions ~50% in Bernstein+’95 field in Coma cluster core

Depends on radial range and evolutionary stage of the cluster, large scatter at large radii in HSC survey (Huang+17)

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ICL properties in individual clusters

  • ICL surface brightness profile shape

varies between clusters - Krick & Bernstein 2007

  • Ellipticity generally increases with

radius, position angle sometimes has sharp variations - Gonzalez + 2005

  • Suggests ICL is dynamically young

and separate from BCG

1 10 100 (kpc/h) PA (o) 50

  • 50

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

ICL optical color: it varies, some red, some blue. Recent phot. in nearby clusters show strong blueward gradient (Mihos+17, Huang+17) Infrared emission: identical to the normal stellar population (ICL is not comprised of brown dwarfs) Bright galaxies tend to have more extended halos with mass (Kormendy+09, Huang+13, 17)

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Observing ICL is difficult…

Because:

  • 1. The signal is, at best, five magnitudes fainter than the night sky
  • 2. Many systematic effects can swamp the results you wish to
  • btain
  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Obstacle: Sky subtraction

The effect of a 0.01% error in sky subtraction at faint magnitudes (Gonzalez et al. 2000) The exact method of sky subtraction (adopting a constant, fitting a plane,

  • r adopting a higher-order function)

differs between research groups.

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Observing ICL is difficult…

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Obstacle: Flat fielding

Flat-fielding to a precision of 0.1% is critical. Dark-sky flats with little scattered light or drift scanning observations

Because:

  • 1. The signal is, at best, five magnitudes fainter than the night sky
  • 2. Many systematic effects can swamp the results you wish to
  • btain
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Observing ICL is difficult…

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Obstacles – Determining the large-scale PSF, and reducing scattered light

The PSF of any object goes out a great distance. At large radii, the profile is caused by dust and imperfections in the telescope . Scattered light from bright stars must be removed from the images, masked (or both). Beware of red halos!! Extensive discussion in Sandin 2015 A&A, 557,106, & red halo effect in SDSS (Tal & van Dokkum 2011)

In this example, by Krick & Bernstein (2007), the PSF has a complex structure.

By careful baffling, the scattered light profile can be significantly reduced.

Because:

  • 1. The signal is, at best, five magnitudes fainter than the night sky
  • 2. Many systematic effects can swamp the results you wish to
  • btain
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Observing ICL is difficult…

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Obstacle: Separating the ICL from the BCG/cD/Other Galaxies

Example data from Seigar et al. (2007) Uson+1991’s approach: …``Whether this diffuse light is called the cD envelope or diffuse intergalactic light is a matter of semantics; it is a diffuse component which is distributed with elliptical symmetry about the center

  • f the cluster potential.’’…

Or work harder…..

Because:

  • 1. The signal is, at best, five magnitudes fainter than the night sky
  • 2. Many systematic effects can swamp the results you wish to
  • btain
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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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BCGs & ICL

Dressler 1979, ApJ, 231, 659:

….Spectra of the envelope of the cD galaxy in the rich cluster of galaxies Abell 2029 out to over 100 kpc are analyzed by using a Fourier cross-correlation

  • technique. It is found that the measured

velocity dispersion apparently increases with radius, implying that the M/L ratio of the envelope is increasing rapidly.

NGC 6616: single

  • Sersic. ICL

clearly signaled by  increase Kelson+01, Bender+15

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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▪ Disentagle cD from ICL in clusters - use the velocity distribution of stars to classify then according to their binding energy (Dolag+10,Cui+14). ▪ Simulations of clusters - VD is bimodal. Fit by two Maxwellians distribution, one narrower (colder) for the central galaxy and a broader one (hotter) for the ICL. ▪ Hotter component is responsible for the “light excess” at large radii. ▪ Stellar particles in hydrodynamical cosmological simulations thus selected turn

  • ut to have different spatial distribution & star formation history.

See also Kapferer et al., 2010, MNRAS, 516, 41.

Kinematics measurement can tag galaxy and ICL stars from their LOSVD at the same spatial location !

Dolag+2010

BCGs & ICL

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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BCGs & ICL : resolved stellar population and spectroscopy

Examples: M87 and ICL in Virgo core M49 and IGL in Virgo subcluster B Coma …. But also NGC 1399 in Fornax and NGC 3311 in Hydra….

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

Mihos et al. 2005, ApJ, 631, L41 And this is where it all started: 3 PNs at vmean ~ 1400 kms-1 along the LOS to NGC 4406 (vsys = - 240 kms-1 ) Arnaboldi, Freeman, et al. 1996, ApJ, 472, 145

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BCGs & ICL : M87 and ICL in the Virgo core

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Spectroscopic follow-up with FLAMES@UT2 on VLT; 288 spectr. confirmed

  • PNs. Additional 12 PNs

from D09 Using their vlos PNs can be classified as M87 halo or intracluster!

Red Gaussian : M87 halo; 225 PNs Blue Gaussian: ICL in Virgo core; 73 ICPNs Line of sight velocity distribution of 300 PNs

M87 Halo vsys = 1275 km/s σn~300 km/s ICL vave = 995 km/s σb~ 900 km/s

Different kinematic components in the Virgo core

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Arnaboldi+2004, ApJL, 614, 33 Doherty+2009, A&A, 502,771 Longobardi+2015a, A&A,579,135, Longobardi+2015b,A&A,579,L3 Longobardi+2018 A&A, sub. Longobardi+2015,A&A, 579,135

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Halo PNs and ICPNs have different spatial distributions: halo PNs have a steeper radial gradient; ICPNs  Rϒ with ϒ=[-0.79 0.15]

* M87 halo PNs * ICPNs

Different kin. & spatial components in the Virgo core

  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Projected phase space diagram vlos vs Rmaj for spec. conf. PNs

+µV K09 Number density profiles

M87 halo PNs

  • ICPNs

Longobardi+2018,A&A, sub Longobardi+15a,A&A, 579,135

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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William et al. 2007, ApJ, 656, 756 Less then 20% of the stars in the VIRGO IC field have ages < 10 Gyrs More than 80% of the stars have ages > 10 Gyrs HST/ACS data for IC field in Virgo, half way between M87 and M86; 36 orbits. Most of the stars with e ages > 10 Gyrs have [M/H] <-1.0

Different populations in the Virgo core

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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Different kin. & spatial components in the Virgo sub. Cluster B – M49

NGC 4472 (M49) BCG at the center of Virgo subcluster B

Capaccioli+2015, A&A,581,10

495 PNs with LOSVs from Hartke+2018arXiv180503092 & Pulsoni+2017arXiv171205833 Poster by J. Hartke and talk by C. Pulsoni this conference

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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  • Bin-free double-Gaussian

model

– Halo: σ = 170 km/s – IGL: σ = 400 km/s

Different kin. & spatial components in the Virgo sub. Cluster B – M49

Hartke+2017, A&A, 603, 104 Pulsoni+2017arXiv171205833 Hartke+2018arXiv180503092

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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  • 37 PNs detected
  • Their LOSVD is not a single Gaussian
  • Multi peaked – secondary bluer peak associated

with nearby substructure G7

  • Main peak of the PN LOSVD is at 6450 kms-1
  • Coma core is not virialized

NGC 4889 NGC 4874 NGC 4889 NGC 4874

NGC 4874 0 = 300 kms-1 NGC 4889 0 = 400 kms-1

Different kin. & spatial components in Coma core

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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  • 37 PNs detected
  • Their LOSVD is not a single Gaussian
  • Multi peaked – secondary bluer peak associated

with nearby substructure G7

  • Main peak of the PN LOSVD is at 6450 kms-1
  • Coma core is not virialized

NGC 4889 NGC 4874 NGC 4889 NGC 4874

NGC 4874 0 = 300 kms-1 NGC 4889 0 = 400 kms-1

We measure the vLOS of stars in the diffuse stellar halo in a region near to NGC 4874, but stars’ vLOS histogram is peaked at -700 kms-1 from its systemic velocity - Halo velocities are flipped!

Gerhard+2005,2007; Arnaboldi+2007

Different kin. & spatial components in Coma core

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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  • 37 PNs detected
  • Their LOSVD is not a single Gaussian
  • Multi peaked – secondary bluer peak associated

with nearby substructure G7

  • Main peak of the PN LOSVD is at 6450 kms-1
  • Coma core is not virialized

NGC 4889 NGC 4874 NGC 4889 NGC 4874

NGC 4874 0 = 300 kms-1 NGC 4889 0 = 400 kms-1

We measure the vLOS of stars in the diffuse stellar halo in a region near to NGC 4874, but stars’ vLOS histogram is peaked at -700 kms-1 from its systemic velocity - Halo velocities are flipped!

Gerhard+2005,2007; Arnaboldi+2007

Different kin. & spatial components in Coma core

Gerhard et al. 2007, A&A,468, 815

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  • M. Arnaboldi – Observations of the ICL MPIA, July 2 2018

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  • Diffuse light in cluster cores ubiquitous – deep photometry and kinematics

from PNs show it is made up of genuine ICL and extended, luminous halos

  • f BCGs. On average, ICL contains ~10% of cluster stellar light, BCG halos

further ~10%; substantial variations depending on cluster evolutionary state.

  • Kinematics from PNs show that ICL is un-relaxed with discrete velocity

components (Virgo, Coma, Hydra) over cluster  scale. BCG halos are colder; constant (NGC 4889), decreasing (M87, NGC 1399), or increasing (Hydra, collapsed ICL) ’s. Together with morphology: dynamically distinct components.

  • Formation of ICL and outer halos, how and when? Evidence for BCG

mergers (Coma+) and tidal disruption/accretion (M87, M49, Hydra) in cluster cores – build-up of BCG halos and nearby ICL continues. Formation

  • f ICL and outer halos on-going and long-lasting process.
  • Stellar population characteristics of the halos and the ICL? – Current results for

Virgo show they are distinct. More work needed : with ELT Coma will become

  • ur backyard & lots to learn!
  • 6. Conclusions