J/AJ/170/342 N(HI) in the local interstellar medium (Youngblood+, 2025)
Toward a 2D HI map of the local interstellar medium.
Youngblood A., France K., Koskinen T., Mason J.P., Redfield S., Wood B.E.,
Bourrier V., dos Santos L., Johns-Krull C., King G.W., Linsky J.L.,
Peacock S.
<Astron. J., 170, 342 (2025)>
=2025AJ....170..342Y 2025AJ....170..342Y
ADC_Keywords: Interstellar medium; H I data; Spectroscopy; Ultraviolet; Optical;
Extreme UV sources; X-ray sources
Keywords: Interstellar absorption ; Extreme ultraviolet astronomy
Abstract:
Obtaining a complete census of gas in the local interstellar medium
(LISM; <100pc) is challenging given the limited available tracers of
the warm, partially ionized medium. Medium- to high-resolution UV
absorption spectroscopy toward individual nearby stars is the primary
method used, and incomplete spatial sampling of this complex medium
makes a global map of the material difficult. Using HI column density
measurements derived from HI Lyα spectroscopy toward 164 stars
inside 100pc, we have generated 2D spatially interpolated N(HI) maps
for different distance shells. Based on the area-weighted sky
averages, we find that sight lines inside 10pc typically have
log10(N(HI)/cm-2)∼17.9. For greater distance shells,
log10(N(HI)/cm-2) increases to 18.3 (10-20pc), then to 18.4
(20-70pc), and finally to 18.6 (70-100pc). This last increase is
likely associated with the detection of the Local Bubble boundary,
thus making the plateau of column density from 20 to 70pc notable and
suggestive of the rarity of warm LISM material beyond ∼10-20pc. We
estimate that the uncertainties associated with N(HI) values inferred
from the interpolated sky maps are approximately inversely correlated
with the number of samples in each distance shell, and are in the
range of 0.20-0.48dex, compared to the 0.01-0.30dex typically
determined from direct Lyα observations. We discuss the impact
of these uncertainties on interstellar medium corrections of
extreme-UV and Lyα observations for nearby stars. Denser spatial
sampling of the sky via UV absorption spectroscopy of nearby stars is
required to improve the accuracy of these N(HI) estimates.
Description:
We assembled N(HI) measurements of stars within 100pc based on
medium- to high-resolution Lyα observations (R∼10,000-110,000)
with the Hubble Space Telescope (HST). Most measurements come from the
literature, and a dozen are drawn from works in preparation. We focus
on the Goddard High-Resolution Spectrograph (GHRS) and the Space
Telescope Imaging Spectrograph (STIS) instruments and exclude Cosmic
Origins Spectrograph (COS) data.
The GHRS was designed to take spectral observations of astrophysical
sources from 1150 to 3200Å. The instrument was removed from HST
during Servicing Mission 2 in February, 1997. STIS is a versatile
imaging spectrograph, providing spatially resolved spectroscopy from
1150 to 10300Å at low to medium spectral resolution, high spatial
resolution echelle spectroscopy in the UV, solar-blind imaging in the
UV, time-tagging of photons for high time resolution in the UV, and
direct and coronagraphic imaging in the optical. STIS operated from
1997 to 2004, and resumed operations in 2009.
To avoid giving individual sight lines with extremely small
uncertainties undue influence on the derivation of the N(HI) maps, we
have imposed a minimum uncertainty of 0.3dex for all N(HI) values
derived from R=10,000-20,000 spectra (instrument modes: STIS/G140M,
GHRS/G140M, GHRS/G160M), and of 0.1dex for the values derived from
R>40,000 spectra (instrument modes: GHRS/ECH-A, STIS/E140M, STIS/E140H).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 89 164 Target list and N(HI) values
--------------------------------------------------------------------------------
See also:
II/203A : Second Extreme Ultra-Violet Explorer Catalog (2EUVE, 1997)
III/135A : Henry Draper Catalogue and Extension (Cannon+ 1918-1924; ADC 1989)
IV/39 : TESS Input Catalog version 8.2 (TIC v8.2) (Paegert+, 2021)
IX/35 : Second EUVE Catalogues (Bowyer+, 1996-99)
J/MNRAS/274/1165 : The 2RE Source Catalogue (Pye+ 1995)
J/A+A/510/A54 : NaI and CaII interstellar absorption (Welsh+, 2010)
J/A+A/615/A117 : 55 Cnc geocoronal emission lines template (Bourrier+, 2018)
J/ApJ/886/19 : Lya obs. of low-mass stars Ross 825 & 1044 (Schneider+, 2019)
J/A+A/634/L4 : HST/STIS FUV spectra of K2-18 (dos Santos+, 2020)
J/A+A/661/A147 : Gal. interstellar dust Gaia-2MASS 3D maps (Lallement+, 2022)
J/AJ/164/106 : Parameters for 130 sight lines within 100pc (Linsky+, 2022)
J/ApJ/946/98 : HST/COS obs. of main-sequence FGKM dwarfs (Cruz Aguirre+, 2023)
J/ApJS/272/30 : Habitable Worlds Observatory (HWO): 164 targets (Harada+, 2024)
J/AJ/170/26 : Predicted detections of exoplanets using CHES & HWO (Bao+, 2025)
J/AJ/170/147 : Mass-separation constraints for HWO target syst (Painter+, 2025)
J/PASP/137/J4402 : HWO Target Stars & Systems 2025 list (TSS25) (Tuchow+, 2025)
J/AJ/170/293 : HWO: UV & X-ray catalog from archival data (Peacock+, 2025)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- Name Star name (1)
18- 23 F6.2 deg GLON [2.21/358.28] Galactic longitude (1)
25- 30 F6.2 deg GLAT [-84.1/89.58] Galactic latitude (1)
32- 36 F5.2 pc Dist [1.3/98.26] Distance (1)
38- 42 F5.2 [cm-2] [NHI] [17.34/19.53] Log of column density (2)
44- 49 F6.4 [cm-2] e_[NHI] [0/0.66] Uncertainty in log10 (NHI) (2)
51- 54 F4.2 [cm-2] e_[NHI]adj [0.1/0.66] Adjusted uncertainty in log10
(NHI) (3)
56- 60 F5.3 cm-3 nHI [2e-3/0.21] Average volume density
62- 68 F7.5 cm-3 e_nHI [0/0.1] Uncertainty in nHI
70- 75 F6.4 cm-3 e_nHIadj [7e-4/0.14] Adjusted uncertainty in nHI
77- 86 A10 --- Inst Instrument/Grating (5)
88- 89 I2 --- Ref [1/51] Column density reference (4)
--------------------------------------------------------------------------------
Note (1): From the CDS SIMBAD database (Wagner+, 2000A&AS..143....9W 2000A&AS..143....9W).
Note (2): Column densities and uncertainties are from Lyα spectra from
HST STIS or GHRS instruments, as reported in the literature. The
resolving powers (λ/Δλ) of each mode are
approximately 10,000 (STIS/G140M), 15,000 (GHRS/G160M), 20,000
(GHRS/G140M), 45,000 (STIS/E140M), 80,000 (GHRS/ECH-A), 110,000
(STIS/E140H).
Note (3): The adjusted uncertainties impose a minimum uncertainty depending on
the mode's resolving power (0.1dex for R≥45,000 and 0.3dex for
R≤20,000); the adjusted uncertainties are used for deriving the
N(HI) maps.
Note (4): Reference as follows:
1 = Wood+2001 (2001ApJ...547L..49W 2001ApJ...547L..49W)
2 = Linsky+1996 (1996ApJ...463..254L 1996ApJ...463..254L)
3 = Youngblood+2022 (2022ApJ...926..129Y 2022ApJ...926..129Y)
4 = Johns-Krull+, in preparation
5 = Hebrard+1999 (1999A&A...350..643H 1999A&A...350..643H)
6 = Wilson+2025 (2025ApJ...978...85W 2025ApJ...978...85W)
7 = Dring+1997 (1997ApJ...488..760D 1997ApJ...488..760D)
8 = Wood+2021 (2021ApJ...915...37W 2021ApJ...915...37W)
9 = Wood+1998 (1998ApJ...492..788W 1998ApJ...492..788W)
10 = Linsky+1995 (1995ApJ...451..335L 1995ApJ...451..335L)
11 = Wood+1996 (1996ApJ...470.1157W 1996ApJ...470.1157W)
12 = Wood+2005 (2005ApJS..159..118W 2005ApJS..159..118W)
13 = Youngblood+2016 (2016ApJ...824..101Y 2016ApJ...824..101Y)
14 = Redfield+2004 (2004ApJ...602..776R 2004ApJ...602..776R)
15 = Vannier+2025 (2025ApJ...981..102V 2025ApJ...981..102V)
16 = Saur+2018 (2018ApJ...859...74S 2018ApJ...859...74S)
17 = Zachary+2018 (2018ApJ...859...42Z 2018ApJ...859...42Z)
18 = Wood+2000b (2000ApJ...537..304W 2000ApJ...537..304W)
19 = Diamond-Lowe+2024 (2024A&A...689A..48D 2024A&A...689A..48D)
20 = Edelman+2019 (2019ApJ...880..117E 2019ApJ...880..117E)
21 = Wilson+, submitted
22 = Behr+2023 (2023AJ....166...35B 2023AJ....166...35B)
23 = Wood+2000a (2000ApJ...542..411W 2000ApJ...542..411W)
24 = Peacock+, in press
25 = Wilson+2021 (2021ApJ...911...18W 2021ApJ...911...18W)
26 = Wood+2014b (2014ApJ...781L..33W 2014ApJ...781L..33W)
27 = Wood+2014a (2014ApJ...780..108W 2014ApJ...780..108W)
28 = Amazo-Gomez+2023 (2023MNRAS.524.5725A 2023MNRAS.524.5725A)
29 = Garcia Munoz+2020 (2020ApJ...888L..21G 2020ApJ...888L..21G)
30 = Bourrier+2020 (2020MNRAS.493..559B 2020MNRAS.493..559B)
31 = Wood+2024 (2024ApJ...967..120W 2024ApJ...967..120W)
32 = Youngblood+2021a (2021ApJ...911..112Y 2021ApJ...911..112Y)
33 = Gry+2017 (2017A&A...598A..31G 2017A&A...598A..31G)
34 = Schneider+2019 (J/ApJ/886/19)
35 = This work
36 = Wilson+2022 (2022ApJ...936..189W 2022ApJ...936..189W)
37 = Bourrier+2018b (2018A&A...620A.147B 2018A&A...620A.147B)
38 = Piskunov+1997 (1997ApJ...474..315P 1997ApJ...474..315P)
39 = Carleo+2021 (2021AJ....161..136C 2021AJ....161..136C)
40 = Shoda+2024 (2024A&A...691A.152S 2024A&A...691A.152S)
41 = Bourrier+2017 (2017A&A...602A.106B 2017A&A...602A.106B)
42 = Ben-Jaffel+2022 (2022NatAs...6..141B 2022NatAs...6..141B)
43 = dos Santos+2020 (J/A+A/634/L4)
44 = dos Santos+, in preparation
45 = Rockcliffe+2021 (2021AJ....162..116R 2021AJ....162..116R)
46 = Bourrier, private communication
47 = Lemoine+2002 (2002ApJS..140...67L 2002ApJS..140...67L)
48 = Kruk+2002 (2002ApJS..140...19K 2002ApJS..140...19K)
49 = Oliveira+2003 (2003ApJ...587..235O 2003ApJ...587..235O)
50 = Vennes+2000 (2000ApJ...544..423V 2000ApJ...544..423V)
51 = dos Santos+2021 (2021A&A...649A..40D 2021A&A...649A..40D)
Note (5): Hubble Space Telescope (HST) instrument and grating as follows:
GHRS/ECH-A = Goddard High-Resolution Spectrograph, Echelle-A
(FUV, R∼80,000); 16 occurrences
GHRS/G140M = Goddard High-Resolution Spectrograph, grating G140M
(FUV, R∼20,000); 2 occurrences
GHRS/G160M = Goddard High-Resolution Spectrograph, grating G160M
(NUV, R∼20,00); 7 occurrences
STIS/E140H = Space Telescope Imaging Spectrograph, grating E140H
(1140-1700Å, R∼114,000); 6 occurrences
STIS/E140M = Space Telescope Imaging Spectrograph, grating E140M
(1144-1729Å, R∼45,800); 81 occurrences
STIS/G140M = Space Telescope Imaging Spectrograph, grating G140M
(1150-1700Å, R∼10,000); 52 occurrences
--------------------------------------------------------------------------------
History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Robin Leichtnam [CDS] 19-Aug-2026