HI clouds near the Galactic Center:

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1 PHISCC 217 February 7th, Pune HI clouds near the Galactic Center: Possible tracers for a Milky-Way nuclear wind? Enrico Di Teodoro Research School of Astronomy and Astrophysics Australian National University Collaborators: Naomi McClure-Griffiths (RSAA), Felix J. Lockman (NRAO-GBT)

2 Galaxy Ecosystems Galaxies are not closed box! Bath-tub model (Lilly et al., 213) Gas cycle determines galaxy evolution: - accretion from CGM and IGM - gas cooling and star formation - stellar and supernovae feedback Galaxy outflow plays a fundamental role: - powered either by AGN or star-formation - circulates enriched material - provide thermal support for the halo - feedback/quenching

3 Galactic Winds OBSERVATIONS M82 - Outflows commonly observed in the local and high universe - Different gas phases co-exist: ionized, neutral and molecular Westmoquette et al., 25 Bolatto et al., 213 NGC253 Cold and dense gas can survive in filaments THEORY Melioli et al., 213 Tanner et al., 216 Lifetimes depends on - mach number - density contrast - wind temperature Zhang et al., 215

4 Galactic Wind In The Milky Way Our Galaxy has its own wind! Ackermann et al., 214 Giant lobes extending to 8-1 kpc and detected in: - γ-rays (Fermi Bubbles, Su+1) - X-rays (e.g., Kataoka+13) - Mid-infrared (Bland-Hawthorn+13) - Polarised radio (Carretti+13) Bi-conical outflow generated a few 16 years ago by either SF (Crocker+11) or SMBH (Yang+12) Credits to NASA

5 HI Tracing The MW Wind Lockman & McClure-Griffiths, 216 Evidence for a cavity in the HI gas that anticorrelates with γ-ray 5 kpc HI evacuated by wind? or Pre-evacuated cavity? Lockman & McClure-Griffiths, 216 Finding the relics of HI swept up by the wind ATCA HI Data Wind model McClure-Griffiths+13 found 86 clouds at the GC not following rotation Entrained in a wind at ~2 km/s

6 -1 Galactic Latitude (deg) A new Green Bank Telescope survey -1 A new survey with 1 m GBT single-dish telescope to widen McClure-Griffiths+13 work ATCA High sensitivity -5 5 Galactic Longitude (deg) 1 (l,b) region Velocity range (km/s) Spatial resolution (arcmin) Channel width (km/s) Sensitivity (Kelvin) ATCA-GC GASS (HI4PI) (McClureGriffiths+13) (McClureGriffiths+9) ± 4º ± All sky ± GBT (Di Teodoro+, in prep) ± 1º ±

7 Masking the MW disk emission GOAL: detecting and studying anomalous clouds above and below the GC Masking the MW disk by modelling it! Clouds not in the disk CLOUD Disk model: an element in (R, z, θ) with V(R, z, θ) can be easily mapped into the (l, b, VLSR) system: z r D R d b l SUN Rotation curve (Sofue et al. 29) + lagging halo (Kalberla & Dedes, 29) + y R Radial and vertical motions (Kubryk et al., 214) ϕ x θ GC

8 Galactic Longitude (degree) 2 2 GALACTIC DISK ROTATION -2-2 VLSR = 2 km/s Galactic Latitude (degree) -1 1 VLSR = -13 km/s Galactic Latitude (degree) Masking the MW disk emission Galactic Longitude (degree) 2 ANOMALOUS CLOUDS

9 Detection of anomalous clouds Cloud detection: Di Teodoro & Fraternali, 215 3D source finder in 3D-Barolo, derived from Duchamp (Whiting12) Reconstructing sources by identifying peak fluxes and growing pixels at the edges in the 3D observational space Source finder parameters: - A primary threshold of 4xRMS and a secondary threshold 2.5xRMS - Minimum acceptance: 5 pixels in spatial domain (~FWHM of beam) 5 channels in spectral domain (5 km/s) - Maximum acceptance: 1 in Longitude/Latitude 1 km/s

10 Results: source detection GC GC 16 anomalous clouds covering ~ 13 deg2

11 Results: population properties Are these local ISM clouds? - Not rotating with the MW - Only observed in the inner degrees - Very high velocities for local ISM Likely at the GC! GC Three cloud examples - Clear spectral detection - Head tail morphology - Well-fitted by a single Gaussian

12 Results: property distributions VLSR < 35 km/s Δv ~ 5-3 km/s R < ~ 8 pc NHI ~ 5x No correlation between FHWM, R or NHI with latitude (height)

13 Wind kinematic model Describing observed cloud kinematic with a simple a galactic wind model Vw Vw(r) CLOUD z D b Vw(r) SUN r R d y l ϕ x θ R Simplest model defined by 2 parameters: - wind velocity Vw = const - opening angle α = π - 2φ GC

14 Wind kinematic model Vw = 3 km/s Simulation of a wind with 14 particles α 8 8 Top view = 12º Side view 4 4 z (kpc) y (kpc) SUN SUN SUN x (kpc) x (kpc) 4 8

15 Wind parameters Simulating winds with different velocities and opening angles ` 3 km/s < Vw < 4 km/s MCG+13 (~2 km/s) α > 14º OK with MCG+13 Total HI mass in clouds: 5 x 15 Msun Wind luminosity: 2 4 x 139 erg/s Can be supplied by GC with SFR~.1-.2 Ms/yr (Crocker12) Cloud lifetimes: > few x 15 years Challenge for theory. Destruction timescales are generally lower Velocity of the hot component: Vh ~ Vw [3nw/2nc]-1/2 ~ 2 km/s (Martin5)

16 Conclusions - A population of anomalous clouds definitely exists at the GC They can be used to trace the properties of MW wind - Our new GBT survey revealed 16 clouds with kinematics compatible with being entrained in a wind with 3 km/s < Vw < 4 km/s and α > 14º Future developments - Refine kinematic model with more reliable Vw(r) (e.g., Zhang+15) - Run HD simulations of MW wind and compare to cloud observed property distributions (e.g., NHI, Δv ). - Follow-up interferometric observations of a few clouds to resolve their morpho-kinematics and compare to simulations

17 Thank you for your kind attention