HI emission as a tracer of interstellar reddening

I presented our new, HI-based extinction map at the 'Advances in Theoretical Cosmology in Light of Data' conference at Nordita, Sweden.

Transcript

1. HI emission as a tracer
   of interstellar reddening
   in collaboration with B.
   Hensley & O. Doré
   arXiv:1706.00011
   Daniel Lenz
   Advances in Theoretical Cosmology in Light of Data
   July 19
   © 2017 California Institute of Technology. Government sponsorship acknowledged.
   

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2. Which foregrounds do we care about?
   "(…) the name of the game is component separation, not noise
   reduction"
   H.K. Eriksen
   ❖ Dust and synchrotron foregrounds in CMB data
   ❖ De-lensing of CMB data for primordial gravitational waves
   ❖ CIB measurements
   ❖ Extinction for cosmological galaxy surveys
   Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
   2
   

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3. Reddening
   

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4. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
   E(B-V)
   ❖ E(B-V) = Extinction in B band - Extinction in V band
   ❖ More dust => larger E(B-V)
   ❖ E(B-V) maps essential for correcting observations for
   Galactic reddening
   4
   

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5. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
   Mapping E(B-V): Direct approach
   ❖ Find many sources with
   known spectrum (e.g.
   stars, passive galaxies)
   ❖ Measure spectra, attribute
   differences to dust
   ❖ E.g. Schlafly+ 2014 used
   500 million stars from
   Pan-STARRS to measure
   reddening to 4.5 kpc
   ❖ Direct measurements are
   hard!
   ❖ Photometric/
   spectroscopic errors
   ❖ Ensuring sources lie
   behind full dust column
   ❖ Ensuring adequate
   number of sources have
   been measured
   5
   

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6. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
   Dust emission as measure of E(B-V)
   ❖ E(B-V) is proportional to the
   dust column, so can convert
   dust column tracer to E(B-V)
   ❖ SFD used dust emission from
   IRAS to derive a calibration
   factor from FIR emission to
   E(B-V)
   ❖ Full-sky, high sensitivity
   measurements
   -2 -0.3
   log10
   (E(B V )SFD
   [mag])
   Reddening map of Schlegel, Finkbeiner,
   and Davis (1998)
   6
   

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7. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
   The SFD reddening map
   ❖ Requires a temperature
   correction to go from dust
   emission to a dust column
   density
   ❖ FIR emission may have
   contributions from Zodiacal
   Light and unresolved galaxies
   -2 -0.3
   log10
   (E(B V )SFD
   [mag])
   Reddening map of Schlegel, Finkbeiner,
   and Davis (1998)
   7
   

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8. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
   The SFD reddening map
   ❖ Requires a temperature
   correction to go from dust
   emission to a dust column
   density
   ❖ FIR emission may have
   contributions from Zodiacal
   Light and unresolved galaxies
   -2 -0.3
   log10
   (E(B V )SFD
   [mag])
   Reddening map of Schlegel, Finkbeiner,
   and Davis (1998)
   7
   

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9. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
   HI emission as basis for E(B-V)
   ❖ Gas and dust are well-coupled in the ISM
   ❖ Perform an SFD-like analysis to convert HI emission to
   E(B-V)
   ❖ Resulting maps free from errors due to dust
   temperature, Zodi, and extragalactic emission
   ❖ Limited by non-HI gas along the line of sight
   8
   

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10. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
    HI4PI Survey
    ❖ Merges data from Effelsberg and Parkes
    ❖ Replaces LAB as state-of-the-art full-sky HI survey
    ❖ Higher sensitivity & resolution, fewer systematics, full sampling
    20
    21
    22
    log(NHI
    [cm 2])
    180
    135 90
    45
    0
    315
    270
    225 180
    60
    30
    0
    30
    60
    HI4PI collaboration

    (2017)
    9
    

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11. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
    1020 1021 1022
    NHI [cm 2]
    10 3
    10 2
    10 1
    100
    E(B V ) [mag]
    0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
    NHI [cm 2] ⇥1020
    0.00
    0.01
    0.02
    0.03
    0.04
    0.05
    0.06
    0.07
    0.08
    E(B V ) [mag]
    E(B V ) [mag] = 1.216+0.009
    0.009
    ⇥ NHI [1022 cm 2] + 0.015+0.0002
    0.0002
    [mag] = 0.02406+0.00006
    0.00006
    100
    101
    102
    103
    104
    # data points
    0
    10
    20
    30
    40
    50
    60
    70
    80
    # data points
    1020 1021 1022
    NHI [cm 2]
    10 3
    10 2
    10 1
    100
    E(B V ) [mag]
    0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
    NHI [cm 2] ⇥1020
    0.00
    0.01
    0.02
    0.03
    0.04
    0.05
    0.06
    0.07
    0.08
    E(B V ) [mag]
    E(B V ) [mag] = 1.113+0.002
    0.002
    ⇥ NHI [1022 cm 2] + 0.000+0.0001
    0.0001
    [mag] = 0.00570+0.00001
    0.00001
    100
    101
    102
    103
    104
    # data points
    0
    100
    200
    300
    400
    # data points
    The E(B-V)/NHI ratio
    Pan-STARRS E(B-V), Schlafly+ (2014) SFD E(B-V)
    Star-based Dust-based
    10
    

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12. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
    1020 1021 1022
    NHI [cm 2]
    10 3
    10 2
    10 1
    100
    E(B V ) [mag]
    0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
    NHI [cm 2] ⇥1020
    0.00
    0.01
    0.02
    0.03
    0.04
    0.05
    0.06
    0.07
    0.08
    E(B V ) [mag]
    E(B V ) [mag] = 1.216+0.009
    0.009
    ⇥ NHI [1022 cm 2] + 0.015+0.0002
    0.0002
    [mag] = 0.02406+0.00006
    0.00006
    100
    101
    102
    103
    104
    # data points
    0
    10
    20
    30
    40
    50
    60
    70
    80
    # data points
    1020 1021 1022
    NHI [cm 2]
    10 3
    10 2
    10 1
    100
    E(B V ) [mag]
    0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
    NHI [cm 2] ⇥1020
    0.00
    0.01
    0.02
    0.03
    0.04
    0.05
    0.06
    0.07
    0.08
    E(B V ) [mag]
    E(B V ) [mag] = 1.113+0.002
    0.002
    ⇥ NHI [1022 cm 2] + 0.000+0.0001
    0.0001
    [mag] = 0.00570+0.00001
    0.00001
    100
    101
    102
    103
    104
    # data points
    0
    100
    200
    300
    400
    # data points
    The E(B-V)/NHI ratio
    Pan-STARRS E(B-V), Schlafly+ (2014) SFD E(B-V)
    Star-based Dust-based
    10
    

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13. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
    0 0.05
    E(B V )model
    [mag]
    The E(B-V) map
    40% sky coverage, 16.1’ resolution
    Lenz, Hensley, Doré
    (2017, submitted)
    11
    

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14. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
    -0.01 0.01
    SFD - PG10 [mag]
    Dust systematics
    ❖ Peek & Graves (2010) used
    SDSS passively evolving
    galaxies as "standard crayons"
    ❖ Correction to the SFD map at
    4.5 deg
    12
    

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15. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
    Dust systematics
    -0.01 0.01
    SFD - PG10 [mag] -0.01 0.01
    SFD - Model [mag]
    13
    Based on extragalactic sources Based on galactic HI
    

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16. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
    HI systematics
    20 40 60 80
    |b| [deg]
    0.04
    0.02
    0.00
    0.02
    0.04
    SFD Model [mag]
    100
    101
    102
    103
    104
    105
    # data points
    1 2 3 4
    NHI [1020 cm 2]
    0.04
    0.02
    0.00
    0.02
    0.04
    SFD Model [mag]
    100
    101
    102
    103
    104
    105
    # data points
    14
    Investigate systematics due to complex ISM physics
    

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17. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
    Model extensions
    ❖ Several large-scale data sets
    available, all of which do not
    significantly improve the
    model
    ❖ A future work would need to
    combine multiphase gaseous
    data, FIR dust data, and Pan-
    STARRS/Gaia data
    0.5 1.0 1.5 2.0
    WCO [K km s 1]
    0.04
    0.02
    0.00
    0.02
    0.04
    SFD Model [mag]
    0.5 1.0 1.5 2.0 2.5 3.0
    SCII [nW m 2 sr 1]
    0.04
    0.02
    0.00
    0.02
    0.04
    SFD Model [mag]
    1 2 3 4
    H↵ [Rayleighs]
    0.04
    0.02
    0.00
    0.02
    0.04
    SFD Model [mag]
    100
    101
    102
    103
    104
    105
    # data points
    15
    

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18. Daniel Lenz, Caltech/JPL An improved, unbiased E(B-V) map
    When and why to use this extinction map
    ❖ New HI based extinction map
    ❖ In line with independent corrections, but much higher
    resolution and better sky coverage
    ❖ Yahata+ (2007) find correlation of SFD with large-scale
    structure
    ❖ For high latitudes, our map overcomes many of the SFD
    problems and is much more sensitive than stellar data-
    based E(B-V) maps
    16
    

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