RR Lyrae as probes of structure in the southern galactic halo




Gabriel Torrealba Arancibia


4 June, 2014

Outline

  • Motivation
  • Catalina Sky Survey
  • RRab Selection Mechanism
  • Sub-Structure
  • Summary

Local tests of the LCDM Paradigm


Bullock & Johnston

Observed Field of Streams

Belokurov (2013)

Recent Discoveries from new Surveys

A mixed bag of Stellar Tracers

  • Main Sequence Turn Off
  • Large amount, ubiquitous, poor distance indicators

  • Blue Horizontal Branch
  • Bright, good distance estimators, metal poor, BS contamination

  • M Giants
  • Very Bright, metal rich, poor distance estimators, rare

  • RR Lyrae
  • Bright, good distance estimators, little contamination, rare, needs variability information

RR Lyrae as tracers


  • Old (>10 Gyr) and Metal Poor
  • Horizontal Branch
  • Bright (V ~ 21 at 110 kpc)
  • Variable stars (P ~ 0.6)
  • distinct light curves
  • \( M_{V} = 0.43 - 0.41 \log(P/P_{0}) \)
  • \( ( \sigma = 0.03) \)

Catalina: All sky variability survey

  • Three Telescopes - Unfiltered Magnitudes
  • CSS + MLS -> Northern telescopes
  • SSS -> Southern telescope
  • Covers 14800 deg2
  • Declination range between -75 and 0
  • 2 arcsec pixels
  • \(\sim\) 100 epochs per star
  • Magnitude range: 11 < V < 19

SDSS Footprint

Catalina Footprint

From Image to RRab

  • Survey data release contains unique discrete sources (\(\sim\) 198 M for CSS)
  • Variability check using Welch-Stetson variability index (\(\sim\) 8.7 M or 4.4%)
  • Periodicity check using Lomb-Scargle Periodogram (23,346 for CSS, \(\sim\) 20,000 for SSS)
  • Lightcurve fitting to get 90% correct periods

Lightcurve Fitting

\( F=\left( \frac{\chi^{2}_{1}}{\chi^{2}_{2}}-1\right)\frac{b}{a} \)

From Image to RRab

  • Survey data release contains unique discrete sources (\(\sim\) 198 M for CSS)
  • Variability check using Welch-Stetson variability index (\(\sim\) 8.7 M or 4.4%)
  • Periodicity check using Lomb-Scargle Periodogram (23,346 for CSS, \(\sim\) 20,000 for SSS)
  • Lightcurve fitting to get 90% correct periods
  • Select RRab based on Lightcurve shape

Lightcurve shape selection

\( M_{t}=\frac{M_{max}-M_{mean}}{M_{max}-M_{min}} \)

10,540 RRab stars

8869 new discoveries!

\( \sim \) 70 % complete within 30 kpc in the south

In the south only!


Around 24000 in the whole sky!

Map of RR Lyrae on the sky

Red is far-away

Blue is nearby

Application 1: Resolve along the line of sight

Application 2: Test large scale asymmetry

Conclusions

Data mine Catalina survey for RR Lyrae

Created the largest sample of RR Lyrae in the South to date

Measured streams like Sagittarius in 3D

RR Lyrae powerful tools to probe the halo

Future Work

Spectroscopic follow up of the overdensities

Go fainter!

Quantify Large Scale Asymmetries.