The Difguse radio emission and Dark Matter Marco Regis (Torino) - - PowerPoint PPT Presentation

Marco Regis (Torino)

The Difguse radio emission and Dark Matter

The ARCADE excess

As we heard in previous talks, quite diffjcult to get rid of it!

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

faint (<µJy), difguse (Mpc scale) and/or exceptionally numerous population (or truly difguse/high-z cosmological sources)

Fornengo,MR+ JCAP 2014

Possible explanations:

I) Observations: issues on calibration of zero level for the low-frequency maps? disfavoured → Al Kogut, Dale Fixsen’s talks II) Galactic foreground: rather peculiar underhanded aspects? disfavoured → Nicolao Fornengo’s talk III) Extragalactic sources

Proposed interpretations

“New” radio source population taking over in the number counts at mJy level

(Singal+ 2010, Ysard&Lagache 2012, ...)

Galaxies would violate FIR-radio relation.

Fornengo,MR+ PRL 2011

Some “exotic” solutions:

• WIMP DM annihilations (Fornengo+2011, Hooper+ 2012,

Fang&Linden 2015)

• late decay of metastable particle (Cline&Vincent 2013)
• ultracompact minihalos (Yang+ 2013)
• quark nugget dark matter (Lawson&Zhitnitsky 2013)
• cluster mergers (Fang&Linden 2015)
• fast radio transient (Kehayias+ 2015)

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Dark matter interpretation

Synchrotron emission induced by WIMP annihilations is a viable solution

→ see also Tim Linden’s talk

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Fang&Linden 2015

Requires signifjcant substructure contributions and large-scale magnetic fjelds. Constraints from other probes (such as the local e+-e- fmux that would be injected by DM)

Fornengo,MR+ JCAP 2012

Synchrotron radiation from DM

It is an indirect^3 method to probe particle DM: source+propagation+radiation

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

If emitted in a medium with magnetic fjeld → radio continuum difguse emission associated to synchrotron radiation.

Energy corresponding to the peak of synchrotron power (in the monochromatic approximation):

Annihilations (or decays) of WIMP DM particles in astrophysical structures inject fmuxes of electrons and positrons (at GeV-TeV energy).

DM source of e-/e+

Morphology Halo profjle and concentration Substructure distribution Halo/subhalo mass function at small scales e.g. the so called “clumping factor”:

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

differential yield

M R & U l l i

• ,

P R D 2 8

energy in units of DM mass

Plot from Sanchez-Conde talk, 2014

Spectrum of injection

M R + , P R L 2 1 5

Transport of e-/e+

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

γ

e+

Confjnement length << halo size → morphology following DM Confjnement length ~ halo size → morphology reshaped Confjnement length >> halo size → signifjcant fraction of power carried away = WIMP annihilation

γ

e+

γ

e+

Synchrotron emission

DM main halo and subhalos

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Image credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI)

Dark structure

non-thermal population of galactic electrons

Magnetic fjeld

V i a L a c t e a p r

• j

e c t

It afgects both SED and morphology

• f the synchrotron emission

Promising cases

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Dark structure + magnetic fjeld “Traditional” structure with non-quiescient baryonic distribution but large scale magnetic fjeld

Awkward cases

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Dark structure with very feeble magnetic fjeld

(e.g. only cosmological one)

“Traditional” structure with non-quiescient baryonic distribution and with magnetic fjeld following baryons

How to test the DM source

Digging into the unresolved radio background:

• 1-point statistics: P(D)
• 2-point statistics: auto and cross correlation

Deep observations of individual sources:

• Dwarf spheroidal galaxies
• Clusters of galaxies
• Big (and edge-on) galaxies
• Filaments?

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Maps from Fornasa et al., 2013

P(D)

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Observations by (Vernstrom+ 2015) suggest a contribution due to difguse emission above the point-like contribution (at the level of about 40% of the unresolved background)

Fornengo,MR+ 2011

→ see Tessa Vernstrom’s talk

Auto and cross correlations

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Holder 2014 Fornengo&Regis 2014

AUTO CORRELATION CROSS CORRELATION with tracers of the DM distribution Synchrotron signal from particle DM is concentrated at low z → see Gil Holder’s talk

EMU is a deep (~10 mJy/beam rms) radio continuum survey of the entire Southern Sky (below +30 deg) at 1.4 GHz, with a 10 arcsec resolution and sensitive to scales up to ~15 arcmin. It is expected to detect about 70 million galaxies

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

EMU

Correlations with EMU

First ASKAP early science data have been recently released EMU early science cosmology should start this summer Full- project: 1.5 years of telescope time SKA1 EMU

Mancuso+ 2015 Raccanelli+ 2012

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Hot and rapidly evolving fjeld:

SDSS has more than doubled the known Local Group dSphs (25 new discoveries) A dozen of new ultrafaint satellites, mostly coming from DES observations, were discovered in the past couple of years Many more to come from near-future surveys. Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Dwarf spheroidal galaxies

→ The non-thermal emission related to star- formation is expected to be extremely low.

Why to perform radio

• bservations?

Carina dSph Inferred from colour-magnitude diagram

Hernandez et al., 2000

Low level of star formation Metal-poor stellar systems

McConnachie, 2013

Very large mass-to-light ratio → Mass budget largely dominated by DM Promising target for particle DM searches!

McConnachie, 2013 McConnachie, 2013

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Local Group dSph

Observations performed with the Australia Compact Telescope Array in two campaigns (2011 and 2016)

16 cm band, 20-30 hours on each dSph

BootesII, Carina, Fornax, Hercules, ReticulumII, Sculptor , Segue2

(MR et al., MNRAS 2015a, MNRAS2015b, JCAP2014, JCAP 2017)

• long baselines to map background sources
• short baselines for the difguse emission search

See also works from Spekkens et al. for similar searches but with a single dish (Green Bank Telescope)

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

ATCA campaigns

Short-baseline map Source subtraction in UV-plane

→ Source subtraction is necessary to bring the noise down from its confusion level

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Source subtraction

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

WIMP hunt

Bounds are far from the expected non-thermal emission related to star formation (which is in some cases possibly achievable by the SKA)

No signifjcant detection of an extended (few arcmin) emission.

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Limits on difguse emission

Impact on WIMP parameter space

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

S K A p r

• s

p e c t s ( r m s 3 n J y )

Within the next 5-10 years and regardless of the astrophysical assumptions, it should be possible to progressively close in on the full parameter space of WIMPs.

Summary

IF dark matter is made of WIMPs, a synchrotron emission from DM is unavoidable, potentially relevant for the ARCADE excess and in general under the reach of current/near-future radio telescopes.

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Backup slides

DM-induced e+-e- source:

Transport equation for e+-e-:

Synchrotron signal

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Radio emission from particle DM

Radio Synchrotron Background Conference, Richmond, 20/07/2017 Marco Regis

Magnetic fjeld